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Book TS * a 5 
Copyright N°_ 



COPYRIGHT DEPOSIT. 



I* 



TWENTIETH CENTURY TEXT-BOOKS 

EDITED BY 

A. F. NIGHTINGALE, Ph.D., LL.D. 

FORMERLY SUPERINTENDENT OF HIGH SCHOOLS, CHICAGO 



TWENTIETH CENTURY TEXT-BOOKS 



ANIMAL FORMS 



A SECOND BOOK OF ZOOLOGY 



BY 

DAVID S. JORDAN, M. S., M. D., Ph. D., LL. D. 

PRESIDENT OK LELANU STANFORD JUNIOR UNIVERSITY 
AND 

HAROLD HEATH, Ph. D. 

PROFESSOR IN LELAND STANFORD JUNIOR UNIVERSITY 




• . » i 



< ' 4 



NEW YORK 

D. APPLETON AND COMPANY 

1902 



Q v £ 



•*V 



THE LIBRARY OF 

CONGRESS, 

T»wr> OoP'-« R^C^ivPD 

MAY, if 1902 


Copyright entry 

CLASS tfxXXc No. 

i X t4- 

COPY B. 



Copyright, 1902 
By D. APPLETON AND COMPANY 



Piiblighe^ May. 19Q% 
* • . • •• ! . .• • 



■ •• "•"••• 



PREFACE 



The present volume is designed to meet the needs of 
the beginning student of zoology. Accordingly, technical 
and scientific names have been avoided as far as possible, 
and those used are fully explained in the text or elsewhere. 
The opening chapters deal with the characteristics of living 
things, and, in contrasting animals and plants, attempt to 
bring into relief the distinguishing marks of all animals. 
Then follows a discussion of the cell and protoplasm, pre- 
paring the way for the examination of a series of animals 
representative of each of the great groups, from the sim- 
plest to the most complex. These are considered from the 
view-point of structure ; but considerable attention is also 
paid to the functions of their parts, to their habits and life- 
history, so that while the representatives examined are, for 
the sake of simplicity, relatively few in number, they are, it 
is believed, thoroughly typical. Hence, with a knowledge 
of the facts presented, the student should have a broad 
view of the animal kingdom, and a foundation on which to 
base future study and observation. It is perhaps unneces- 
sary to add that from the study of books alone no one can 
really make such knowledge his own. A personal acquaint- 
ance with even a few animals in their native haunts, and 
an understanding of the structure and the function of their 



Vi ANIMAL FORMS 

parts gained from dissection and experiment, is essential to 
a full comprehension of what the student learns from text- 
book and teacher. 

The greater number of illustrations are new, and have 
been drawn or photographed from living or preserved ma- 
terial. When not otherwise accredited, the drawings have 
been made by Miss Mary H. Wellman and J. Carter Beard, 
to whom the authors extend their sincere thanks. Our 
obligations are also due to Mr. Walter K. Fisher, who has 
made the drawings of the vertebrate dissections; to Messrs. 
A. L. Melander and C. T. Brues, of Chicago, 111. ; Mr. Wm. 
H. Fisher, of Baltimore, Md. ; Eev. H. K. Job, of Kent, 
Conn. ; Mr. Wm. Graham, of Pasadena, Cal. ; and Dr. E. W. 
Shufeldt, of New York city, for numerous photographs. 

David Starr Jordan, 
Harold Heath. 



CONTENTS 



CHAPTER PAGE 

I. — Introduction 1 

II. — The cell and protoplasm 7 

III. — The Protozoa 11 

IV. — The sponges 19 

V. — The Ccelenterates 29 

VI. — The worms 44 

VII. — Animals of uncertain relationships . . . .66 

VIII.— Mollusks 72 

IX. — Arthropods. Class Crustacea 93 

X. — Arthropods. Class Insects 114 

XL — Arthropods. Class Arachnida 133 

XII. — ECHINODERMS . 140 

XIII. — The chordates 151 

XIV.— The fishes 154 

XV. — The amphibians 174 

XVI.— The reptiles 184 

XVII.— The birds 201 

XVIII.— The mammals 2£5 

vii 



ANIMAL FORMS 



CHAPTER I 

INTRODUCTION 

1. Divisions of the subject. — Biology is the science which 
treats of living things in all their relations. It is sub- 
divided into Zoology, the science which deals with animals, 
and Botany, which is concerned with plants. The field 
covered by each of these branches is very extensive. 
Within the scope of zoology are included all subjects bear- 
ing on the form and structure of animals, on their devel- 
opment, and on their activities, including the consideration 
of their habits and the wider problems of their distribution 
and their relations to one another. 

These various subjects are often conveniently grouped 
under three heads : Morphology, which treats of the form 
and structure or the anatomy of organisms ; Physiology, 
which considers their activities ; and Ecology, which in- 
cludes their relations one to another and to their surround- 
ings. All the phases of plant or animal existence may be 
considered under one or another of these three divisions. 

2. The difference between animals and plants. — Generally 
speaking, we have little difficulty in seeing that the objects 
about us are either living or lifeless ; but the boundary line 
between the two great divisions of living things, the animals 
and plants, can not always be so clearly drawn. This is es- 
pecially true of the simpler forms of life which frequently 
combine both animal and plant characteristics ; but in the 

1 



2 ANIMAL FORMS 

greater number of more highly developed species the line 
of separation is clearly marked. It is very easy, for example, 
to distinguish the oak-tree or the rose from a horse or a 
butterfly, and, as we shall see, the differences are not based 
merely on outward appearance. 

In the oak-tree, for example, the roots reaching down 
into the earth, with the branches and leaves spreading out 
into the air and sunlight, are admirably fitted for taking up 
the food, which consists of very simple materials, less com- 
plex than those forming the diet of an animal. This 
permits a continuous existence in one place, and accord- 
ingly we note the entire absence of locomotion and the or- 
gans controlling it, which form so conspicuous a part of the 
body of an animal. Also in the production of flowers and 
seeds, and in the growth of the seed into the tree, we detect 
many characteristics peculiar to plants. 

3. Characteristics of an animal. — On the other hand, the 
squirrel, for example, or any other animal, is unable to sub- 
sist on water, air, and elements from the soil. These crea- 
tures demand the highly diversified materials found in the 
bodies of plants and of animals. Such being the case, they 
do not remain anchored to one spot (except in a relatively 
few cases), but are compelled to lead an active existence. 
The power of voluntary movement, or movement in response 
to internal impulse, is thus the first and one of the most 
striking peculiarities of animals. 

In the second place, the food of plants enters the body 
in a soluble condition and is readily transferred to the or- 
gans requiring it. While in the animals, the nutritive ma- 
terials pass into the body in an insoluble state and de- 
mand a varied preliminary treatment, usually within a 
special digestive tube, before they are fit to be absorbed. 
In the squirrel, by way of illustration, the food is first 
ground to a pulp by the action of the teeth, and, moistened 
with saliva, is swallowed and passed into the stomach, 
where it is subjected to the solvent action of the gastric 



ANIMAL FORMS 



juice. From the stomach it is made to enter the intestine, 
and is further acted upon by fluids from the liver, the 

pancreas, and the glands of the 
intestines themselves. Thus 
treated it becomes changed from 
an insoluble state into a fluid 
which readily penetrates the 
coats of the digestive tract. 

Many of the organs of the 
body are placed at a considera- 
ble distance from the food as 
it comes through the coats of 
the stomach and intestine. In 
order to supply them with the 
necessary nourishment a distrib- 
uting apparatus is required. 
This is the office performed by 
the circulatory system, for as 
rapidly as the food penetrates 
the walls of the digestive tract 
it enters the blood, and by the 
beating of the heart is driven 
to all parts of the body, which 
are thus continually kept in a 
state of repair. The blood serves 
also to remove waste substances 
from the various structures or 
organs of the animal body and 
to transfer them to the kidneys, 
skin, or lungs, which effect their 
removal from the body. 

4. Muscular and nervous sys- 
tems. — Owing to the fact that 
animals, as a rule, are compelled 
to move about in search of food, we find two highly devel- 
oped systems, the muscular and nervous, which are absent 




Fig. 2.— Diagram of heart and blood- 
vessels of the squirrel or other 
mammal, a.o., aorta ; h, vessels 
of head ; La., left auricle; Lex., 
vessels <>f lower extremities ; lg., 
lung ; l.v., left ventricle ; p. a., 
pulmonary artery ; />.?'., pulmo- 
nary vein ; /.".. right auricle ; 
. righl ventricle : r.. vessels Oi 
viscera. Arteries are represented 

by heavy walls. 



INTRODUCTION 5 

in the plants. The first of these, constituting what is usu- 
ally known as the lean meat, is a relatively complex system 
of organs, differing widely according to the work performed. 
In the higher animals — the squirrel, for example — there are 
not less than five hundred muscles, which are under the 
control of the nervous system. 

The nervous system consists of the brain and spinal 
cord, which in the squirrel are concealed and protected 




Fig. 3.— Skeleton of squirrel, showing its relation to the body. 

within the skull and back-bone. From them many nerves 
pass outward to the muscles, and as many pass inward from 
the eye, ear, nose, tongue, or skin. By the action of these 
sense-organs the animal determines the nature of its sur- 
roundings, detects its food, recognizes the presence of its 
enemies, and is thus able to direct its movements to the 
greatest advantage. 

5. Multiplication of animals. — The organs thus far con- 
sidered serve to perpetuate the animal as an individual ; 
but some provision must also be made for the continuance 
of the race. In the economy of nature each animal before 



6 ANIMAL FORMS 

its death should leave offspring to take the place of the 
parent when it falls from the ranks. This is effected in 
various ways. In some of the simpler animals the body- 
may divide into two equal parts, each of which becomes a 
complete individual. In other cases the animal detaches 
a relatively small portion of its body, much as a gardener 
cuts a slip from a plant, and this likewise develops into a 
new organism. In the greater number of animals, very 
clearly illustrated by the birds, eggs are produced which 
under favorable conditions develop into an organism resem- 
bling the parents. 

6. Summary. — Animals are thus seen to lead active, busy 
lives, collecting food, avoiding enemies, and producing and 
ao£ caring for their young. While the activities of all 
animals are directed to their own preservation and to the 
multiplication of their kind, these processes are carried on 
in the most diverse ways. The manner in which an organ 
or an organism is made, and the method by which it does 
its work, are mutually dependent one on the other. As 
there is an enormous number of species of animals, each 
differently constructed, there is, accordingly, a very great 
variety of habits. As we shall see, the lower forms are 
remarkably simple in their construction, and their mode of 
existence is correspondingly simple. In the higher types 
a much greater complexity exists, and their activities are 
more varied and are characterized by a high degree of elabo- 
ration. In every case, the animal, whether high or low, is 
fitted for some particular haunt, where it may perform its 
work in its own special way and may lead a successful life 
of its own characteristic type. 



CHAPTER II 



THE CELL AND PROTOPLASM 



7. Cells. — If we examine very carefully the different parts 
of a squirrel under the high powers of the microscope 
we find that they are composed of a multitude of small 
structures which bear the same relations to the various 
organs that bricks or stones do to a wall ; and if the inves- 
tigation were continued it would be found that every or- 
ganism is composed of one or more of these lesser elements 
which bear the name of cells. In size they vary exceedingly, 
and their shapes are most diverse, but, despite these differ- 
ences, it will be seen that all exhibit a certain general re- 
semblance one to the other. 

8. Shape of cells. — In many of the simpler organisms 
the component cells are jelly-like masses of a more or less 
spherical form, but as we ascend the scale of life the condi- 
tion of affairs becomes much more complex. In the squir- 
rel, for example, we have already noted the presence of 
various organs for carrying on different functions, such as 
those of digestion, circulation, and respiration; and, further, 
the cells composing these various parts have been modified 
in accordance with the duties they have to perform. In 
the muscles the cells are long and slender (Fig. 4, D) ; 
those forming the nerves and conveying sensations to and 
from all parts of the body, like an extensive telegraph sys- 
tem, are excessively delicate and thread-like ; in the skin, 
and lining many cavities of the body, where the cells are 
united into extensive sheets, they range in shape from high 
and columnar to flat and scale-like forms (Fig. 4, E, F, G). 



8 ANIMAL FORMS 

The cells of the blood present another type (Fig. 4, B) ; and 
so we might pass in review other parts of the body, and con- 
tinue our studies with other groups of animals, always find- 
ing new forms dependent upon the part they play in the 
organism. 

9. Size of cells. — Also in the matter of size the greatest 
variations exist. Some of the smallest cells measure less 
than one micromillimeter (^-J-qo of an inch) in diameter. 
Over five hundred million such bodies could be readily 
stowed away into a hollow sphere the size of the letter be- 
ginning this sentence. In a drop of human blood of the 
same size, between four and five million blood-cells or cor- 
puscles float. And from this extreme all sizes exist up to 
those with a diameter of 2.5 or 5 cm. (one or two inches), 
as in the case of the hen's or ostrich's egg. On the average 
a cell will measure between .025 to .031 m.m. ( T oVo an( i 
-g^o of an inch) in diameter, a speck probably invisible to 
the unaided eye. While the size and external appearance 
of a cell are seen to be most variable, the internal structures 
are found to show a striking resemblance throughout. All 
are constructed upon essentially the same plan. Differ- 
ences in form and size are superficial, and in passing to a 
more careful study of one cell we gain a knowledge of the 
important features of all. 

10. A typical cell. — Some cell, for example that of the 
liver (Fig. 4, A), may be chosen as a good representative of 
a typical cell. To the naked eye it is barely visible as a 
minute speck ; but under the microscope the appearance is 
that of so much white of egg^ an almost transparent jelly- 
like mass bearing upon its outer surface a thin structure- 
less membrane that serves to preserve its general shape and 
also to protect the delicate cell material within. The com- 
parison of the latter substance to egg albumen can be car- 
ried no further than the simple physical appearance, for 
albumen belongs to that great class of substances which 
are said to be non-living or dead, while the cell material 



THE CELL AND PROTOPLASM 



9 



or protoplasm, as it is termed, is a living substance. We 
know of no case where life exists apart from protoplasm, 
and for this reason the latter is frequently termed the 
physical basis of life. 

In addition to the features already described, the proto- 
plasm of every perfect cell is modified upon the interior to 




Fig. 4.— Different types of cells composing the body of the squirrel or other highly 
developed animal. A, liver-cell ; /, food materials ; n, nucleus. B, blood-cell. 
C, nerve-cell with small part of its fiber. D, muscle fiber. E, cells lining the 
body cavity. F, lining of the windpipe. G, section through the skin. Highly 
magnified. 



form a well-defined spherical mass known as the nucleus. 
Other structures are known to occur in the typical cell. 
Experiment shows that the nucleus and cell protoplasm arc 
absolutely indispensable, whatever their size and shape, and 



10 ANIMAL FORMS 

therefore we are at present justified in defining the cell as 
a small mass of protoplasm enclosing a nucleus. 

11. Structure of protoplasm. — When seen under a glass 
of moderate power protoplasm gives no indication of any 
definite structure, and even with the highest magnifica- 
tion it presents appearances which are not clearly under- 
stood. According to the commonly accepted view, it con- 
sists of two portions, one, the firmer, forming an excessively 
delicate meshwork (Fig. 4, A) enclosing in its cavities 
the second more fluid part. Therefore, when highly mag- 
nified, the appearance would be essentially like a sponge 
fully saturated with water ; but it should be remembered 
that in the protoplasm the sponge work, and possibly the 
fluid part, is living, and that both are transparent. 

There are reasons for thinking that the structure and 
the composition of protoplasm may change somewhat under 
certain circumstances. It certainly is not everywhere alike, 
for that of one animal must differ from that of another, and 
different parts, such as the liver and brain, of the same form 
must be unlike. These differences, however, are minor 
when compared to the resemblances, for, as we shall see, 
this living substance, wherever it exists, carries on the pro- 
cesses of waste, repair, growth, sensation, contraction, and 
the reproduction of its kind. 



CHAPTEE III 

THE PROTOZOA 

12. Single-celled and many-celled animals. — In almost 
every portion of the globe there are multitudes of animals 
whose body consists of but a single cell ; while those forms 
more familiar to us, and usually of comparatively large 
size and higher development, such as sponges, insects, 
fishes, birds, and man himself, are composed of a multitude 
of cells. For this reason the animal kingdom has been 
divided into two great subdivisions, the Protozoa including 
all unicellular forms and the Metazoa embracing those of 
many cells. 

13. Single-celled animals. — The division of the Protozoa 
comprises a host of animals, usually of microscopic size, 
inhabiting fresh or salt water or damp localities on land in 
nearly every portion of the globe. The greater number 
wage their little, though fierce, w T ars on one another with- 
out attracting much attention ; others, in the sharp struggle, 
have been compelled to live upon or within the bodies of 
other animals, and many have become notorious because of 
the diseases they produce under such circumstances. A 
few are in large measure responsible for the phosphores- 
cence of the sea ; and still others have long been favorite 
objects of study because of their marvelous beauty. Adapted 
for living under diverse conditions, the bodily form differs 
greatly, and yet all conform to three or four principal types, 
of which we may gain a good idea from the study of a few 
representative forms. 

11 



12 



ANIMAL FORMS 



14. The Amoeba. — Among the simplest one-celled ani- 
mals living in the ooze at the bottom of nearly every fresh- 
water stream or pond is the Amoeba (Fig. 5, A), whose body 
is barely visible to the unaided eye. Under the microscope 




Fig. 5.— A, the Amoeba, highly magnified, showing c. v., pulsating vacuole; /, food 
particle ; n, nucleus. The arrows show the direction of movement. B, shape of 
same individual 30 seconds later. C, an amceba-like animal {Difflugia) partially 
enclosed in a shell. D, an Amoeba in the process of division. E, Gromia, another 
shelled protozoan (after Schulze). 

it is seen to consist of an irregular, jelly-like mass of proto- 
plasm totally destitute of a cell wall. Unlike those animals 
with which we are familiar, the body constantly changes its 
'shape. »A rounded bud-like projection will be seen to appear 
on one side of the body and the protoplasm of adjacent 
regions flows into it, thereby increasing its extent. Similar 
projections at the opposite end of the cell are withdrawn, 
and their substance may flow into the newly formed lobe, 
which gradually swells in size and pushes forward. Thus, 
by constantly advancing the front part of the body and 



THE PROTOZOA 13 

retracting the hinder portion, the cell glides or flows along 
from place to place. 

Upon meeting with any of the smaller organisms upon 
which it lives, projections from the body are put out which 
gradually flow around the prey and it becomes pressed into 
the interior of the cell. The process is not unlike pushing 
a grain of sand into a bit of jelly. There is no mouth. 
Any point on the surface serves for the reception of food. 
Oxygen gas also is taken into the body all over the surface, 
and wastes and indigestible material are cast out at any 
point. Nothing exists in these simple forms comparable to 
the complex systems of organs that carry on these processes 
in the squirrel. 

The bodily size of animals is limited, and to this general 
rule the Amoeba is no exception, for upon gaining a certain 
size, the nucleus divides into two exactly similar portions, 
and very soon afterward the rest of the body separates into 
two independent masses of equal size (Fig. 5, D), each of 
which, when entirely free, contains a nucleus. In this way 
two daughter amoebae are formed possessing exactly the 
characters of the parent save that they are of smaller size ; 
but it is usually not long before they reach their limit of 
growth, when division occurs again, and so on, generation 
after generation. 

It not infrequently happens, however, that the pond or 
stream, in which the Amoeba and other Protozoa live, dries 
up for a portion of the year. In such an event the body 
assumes a spherical shape, develops a firm, horn-like mem- 
brane about itself, and thus encysted it withstands the sum- 
mer's heat and dryness and may be transported by the wind, 
or otherwise, over great distances. When the conditions 
again become favorable the wall ruptures and the Amoeba 
emerges to repeat its life processes. 

15. Some relatives of the Amoeba. — All amoeba-like forms, 
to the number of perhaps a thousand species, possess this 
same method of locomotion, but many present some inter- 



14 ANIMAL FORMS 

esting additional characters. For example, the form repre- 
sented in Fig. 5, C, constructs a sac-like skeleton of tiny- 
pebbles cemented together, into which it may withdraw for 
protection. Others construct similar envelopes of lime or 
flint, and still others, as they continue to grow, build on 
additional chambers, giving rise to a great variety of forms 
often of wonderful beauty. In the tropics, particularly, 
some of the shelled Protozoa are so abundant that they may 
impart a whitish tinge to the water, and in some places 
their empty shells on falling to the bottom form immense 
deposits. The chalk cliffs of England are in large measure 
made up of such shells. 

16. The Infusoria. — A little over two hundred years ago 
it was discovered that wherever water remained stagnant it 
became favorable for the rapid multiplication of a large 
number of species of Protozoa which live in such situations. 
These are known as Infusoria, and, like the preceding spe- 
cies, are usually of microscopic size and of the most varied 
shapes. The first striking feature of their organization is 
the presence of a delicate though relatively firm external 
cell membrane known as the cuticle, which preserves a defi- 
nite shape to the body. Such a method of locomotion as 
exists in the preceding group is consequently an impossi- 
bility, but other and more highly developed structures per- 
form the office. These latter organs are of two types, and 
their general characteristics may be readily understood 

.from an examination of a few species living in the same 
localities as the Amoeba. 

17. The Euglena. — The first type exists in the common 
fresh-water organism known as Euglena, represented in 
Fig. 6, A. Here the spindle-shaped body is surrounded by 
a delicate cuticle perforated at one point, where a funnel- 
shaped depression, the gullet, leads into the soft proto- 
plasmic interior. From the base of this depression the 
protoplasm is draws out in the form of a delicate whip-like 
process known as the jiagcllum. This structure, always 



THE PROTOZOA 



15 



permanent in form, constantly beats backward and forward 
with great rapidity in a general direction represented in 
the diagram (Fig. 6, c). The movement from a to b is 
much more rapid than the reverse, from b to r/, which 
results, like the action of the human arm in swimming, in 
driving the organism forward. Not only does the flagel- 
lum serve the purpose of locomotion, but it also produces 
currents in the water which 
may serve to bear minute 
organisms down into the 
gullet, whence they read- 
ily pass into the soft pro- 




Fig. 6. — Flagellate Infusoria. A, 
Euglena xxridis ; c, pulsating 
vacuole ; e, eye-spot ; g, gullet ; 
ra, nucleus ; t, flagellum. B, Co- 
dosiga, with collar surrounding 
the flagellum. C, diagram illus- 
trating the action of the flagel- 
lum. All figures greatly enlarged. 




Fig. 7. — Paramecium aurelia, a 
ciliate infusorian. c, cilia; c.v.. 
pulsating vacuoles ; /, food 
particles; g, gullet; 771, buccal 
groove ; /?. nucleus. 



toplasm of the body, there to undergo the processes of di- 
gestion and assimilation. In some forms the protoplasm in 
the region of the flagellum is drawn out in the form of a 
collar (Fig. 6, B), whose vibratory motion also aids in con- 
veying and guiding food into the body. 

18. The Slipper Animalcule. — The second type of loco- 
motor organ may be understood from a study of the 



16 



ANIMAL FORMS 



Slipper Animalcule (Paramwcium, Fig. 7), abundant in 
stagnant water. In this form the cuticle surrounding the 
somewhat cylindrical body is perforated by a great number 
of minute openings through which the 
internal protoplasm projects in the form 
of delicate threads. Each process, 
termed a cilium, works on the same 
principle as the flagellum, but it beats 
with an almost perfect rhythm and in 
unison with its fellows, drives the an- 
imal hither and thither with considera- 
ble rapidity. 

On one side of the body is a furrow 
which deepens as it runs backward and 
finally passes into the gullet (#), which 
leads into the interior of the body. 
Throughout the entire extent it is lined 
with cilia which create strong currents 
in the surrounding water and in this 
way conduct food down the gullet into 
the body. Embedded in the outer sur- 
face of the body, in among the cilia, 
are also a number of very minute sacks, 
each containing a coiled thread which 
may be discharged against the body of 
any intruder, so that this form is sup- 
plied with actual organs of defense. 

cuole; g, gullet; n, nu- * ° 

cieus. b, contracted ± wo pulsating vacuoles (c.v.) or simple 
specimen. c,smaiifree- kidneys are also present, consisting of a 
central reservoir into which a number 
of radiating canals extend. 

10. The Bell Animalcule and other 
species. — The Bell Animalcule ( Forth 
cella, Fig. 8) is often found in the same situations as the 
Slipper Animalcule, which in certain respects it resembles. 
It is generally attached by a slender stalk, and where many 




Fig. 8.—Vorticella, an at- 
tached ciliate infusori- 
an, highly magnified, a, 
fully extended individ- 
ual ; c.v., pulsating va- 



swimming individual, 
which unites with a sta- 
tionary individual (One 
partly united [s shown 
in Bpecimen b). 



THE PROTOZOA 17 

are growing together they appear like a delicate growth 
of mold upon the water weed. The stalk is peculiar in 
being traversed by a muscle fiber arranged in a loose spiral, 
which upon any unusual disturbance contracts together 
with the body into the form shown in Fig. 8, b. 

These few examples serve to show the general plan of 
organization and the method of locomotion of the Infuso- 
ria ; but, as upward of a thousand species exist, with widely 
differing habits, many interesting modifications are present. 
Some have been driven in past time to adopt a parasitic 
mode of life within the bodies of other animals. At pres- 
ent they are devoid of locomotor organs, and as they absorb 
nutritive fluids through the surface of the body all traces 
of a mouth are also absent. The reproductive processes 
also are peculiar, but they do not concern us now. 

20. Characteristics common to the Protozoa. — We have 
now studied the principal structures which serve in loco- 
motion among these simple one-celled forms, also the means 
by which they catch their food, and we shall now glance at 
the internal processes, which are much the same in all. 

After the food has been taken into the cell, it is prob- 
ably acted upon by some digestive fluid, for it soon assumes 
a granular appearance and finally undergoes complete solu- 
tion. In every case the oxygen is absorbed through the 
general surface of the body, and uniting with the living 
substance, as in the squirrel, liberates the energy necessary 
for the performance of the animal's life work. The wastes 
thus produced in a large number of forms simply filter out 
from the body without the agency of anything comparable 
to a kidney, but in several species they are borne to a 
definite spot, the pulsating vacuole (Figs. 5, 7, 8, c.v.), where 
they gradually accumulate into a drop about the size of the 
nucleus. The wall between it and the exterior now gives 
way and the excretions are passed out. In active indi- 
viduals this process may be repeated two or three times a 
minute, but it is usually of less frequent occurrence. 



. 



18 ANIMAL FORMS 

The loss in bodily waste is continually made good by 
the manufacture of the food into protoplasm, and if the in- 
come be greater than the outgo growth ensues. But, as in 
all other forms, growth is limited, and ultimately the cell is 
destined to divide, resulting in two new individuals. This 
process may be repeated many times, but not indefinitely, 
for sooner or later various members of the same species 
unite in pairs temporarily or permanently, exchange nu- 
clei r material, and separate again with apparently renewed 
energy and the ability to divide for many generations. 

21. Simple and complex animals. — It is important to note 
that these same processes of waste, repair, growth, feeling, 
motion, and multiplication are the same as those of the 
squirrel, and, furthermore, are common to all living crea- 
tures, so that the difference between animals is not in their 
activities, but in their bodily mechanisms ; and according to 
the perfection of this, the animal is high or low in the 
scale. Comparing, for example, the Amoeba and Slipper 
Animalcule, which are relatively low and high Protozoa, we 
find in the former that any part of the body serves in loco- 
motion and in the capture of food, while in the latter these 
same functions are performed by definite structures, the 
cilia and gullet. Now it is well known that a workman is 
able to make better watch-springs, when this is his sole 
duty, than another who must make all parts of the watch ; 
and likewise where a definite task is performed by a defi- 
nite structure, it is more efficiently done than where any 
and every part of the body must carry it on. So the 
Amoeba, in which definite tasks are performed by any part 
of the body indifferently, is less perfect and thus lower than 
I he ParamoBcium, where these functions are performed by 
special organs. As we ascend the scale of life we find this 
division of labor among special parts of the body more 
complete, the organs and therefore the animal more com- 
plex, and better litled to carry on the work of its life. 



CHAPTER IV 



THE SPONGES 



22. Their relation to the Protozoa. — While the greater 
number of one-celled forms are not united with their fel- 
lows, there are several species where the reverse is true. In 
Fig. 9, for example, a fresh-water form known as Pandorina 
is represented, consisting of sixteen cells embedded in a 
spherical, jelly-like substance, 
each one of which is precisely 
like its companions in form 
and activity. The aggregation 
may be looked upon as a colo- 
ny of sixteen Protozoa united 
together to derive the benefit 
of increased locomotion and 
a larger amount of food in 
consequence. As a result of 
such a union they have not 
lost their independence, for if 
one be separated from the main 
company it continues to exist. 

From such a simple colonial 
type we may pass through a series of several more complex 
forms which reach their highest development in the beau- 
tiful organism, Volvox (Fig. 10). In this form the indi- 
vidual members, to the number of many thousand, are ar- 
ranged in the shape of a hollow sphere. The united efforts 
of the greater number, which bear on their outer surfaces 
two flagella, drive the colony with the rolling movement 

19 




Fig. 9.- 



-Pandorina (from Nature). 
Highly magnified. 



■™ 



20 



ANIMAL FORMS 



from place to place. As just indicated, some individuals 
lack the flagella, and their subsequent careers show them 
to be of a peculiar type. Sooner or later each undergoes 

a series of divisions form- 
ing a little globe of cells, 
which migrates into the in- 
terior of the parent sphere 
and develops into a new 
colony. Within a short time 
the walls of the parent 
break, liberating the im- 
prisoned young, which con- 
tinue the existence of the 
species while the parent or- 
ganism soon decays. 

Under certain circum- 
stances, instead of develop- 
ing colonies by such a meth- 
od, some of the cells may 
store up food matters and 
become eggs, while others, 
known as sperm-cells, de- 
velop a flagellum,.and sep- 
arating from the colony 
swim actively in the sur- 
rounding water, where each 
finally unites with an egg. 
This union, like that of the 
two individuals in Vorticel- 
la (Fig. 8, S, c), results in 
the power of division, and 
the egg enters upon its de- 
velopment, dividing again 
and again. The cells so pro- 
duced remain together, form a sphere, and finally develop 
a Volvox colony. 




Fig. 10.— A, Volvox minor, entire colony 
(from Nature). B, C, and D, reproduc- 
tive cells of Volvox globator. All highly 
magnified. 



THE SPONGES 21 

In such associations as Volvox an important step has 
been taken beyond that of Pandorina, for there is a division 
of the labors of the colony among its various members 
some acting as locomotor cells while others are germ-cells. 
These are now so dependent one upon the other that they 
are unable to exist after separation from the main com- 
pany, just as a part of the squirrel is incapable of leading 
an independent existence. A higher type of organism has 
thus arisen intermediate between the simple one-celled 
animals and those of many cells, especially the sponges — a 
relation which is more readily recognized after an examina- 
tion of the latter. 

23. Development of the sponge. — As with all many- 
celled animals, the sponge begins its existence as an egg, 
in this case barely visible to the sharp unaided eye. Fer- 
tilized by its union with a sperm cell, development com- 
mences, and the first apparent indication of the process 
will be the division of the cell into two halves (Fig. 11, A, B). 
Each half redivides into four, these again into eight cells, 
and this process is repeated, giving the young sponge the 
general form of Pandorina. The divisions of the cells 
still continue and result in the formation of a hollow 
globe of cells (called the blastula, Fig. 11, E, F) similar 
to Volvox, and at this point the young larva leaves the 
parent. 

The next transformation consists in a pushing in of one 
side of the sphere, just as one might press in the side of a 
hollow rubber ball. The depression gradually deepens, and 
finally results in the formation of a two-layered sac known 
as the gastrula (Fig. 11, G). At this stage of its existence 
the sponge settles down for life in some suitable spot, by 
applying the opening of its sac-like body to some foreign 
object. In assuming the final form a new mouth breaks 
through what was once the bottom of the sac, canals per- 
forate the body wall, a skeleton is developed, and the char- 
acteristic features of the adult are thus attained. 



22 



ANIMAL FORMS 



24. Distribution. — The sponges are aquatic animals, and, 
with the exception of one family consisting of relatively 
few species, all are inhabitants of the sea in every part of 




Pig. 11. Diagrams illustrating the development of a sponge. A, egg-cell; ?k nu- 
cleus. II. c. 1), -,»-, 1-, and 16-cell stages. E, blastula. F, section through some- 
what older larvae. Q t ga8trula. II, young sponge. I, section through somewhat 
younger larvae than H. 

the globe. The larger number occupy positions along the 
shore, becoming especially abundant in the tropics; but 
other species occur at greater depths, several species living 



THE SPONGES 23 

between three and four miles from the surface. Unlike 
the majority of animals, all members of this group are 
securely fastened to some foreign object, such as rocks, the 
supports of wharves, or with one extremity embedded in 
the sand. As we have seen, the young enjoy a free-swim- 
ming existence and are swept far and w r ide by means of 
tidal currents, but sooner or later these migrations are 
terminated in some suitable locality, w T here the sponge 
passes the remainder of its existence. During this time 
some species may never exceed the size of a mustard-seed, 
while others attain a diameter of three feet, or even more. 
Sponges also vary exceedingly in shape, some having the 
form of thin encrusting sheets, others being globular, tubu- 
lar, cuplike, or highly branched (Fig. 12). 

25. The influence of their surroundings. — In by far the 
larger number of cases an animal possesses the bodily form 
of the parent. External agencies may modify this to some 
extent, but usually only to a limited degree. A squirrel, 
for example, resembling its parent, may grow to a relatively 
large or stunted size according to the food supply, and it 
may become strong or weak according to the amount of 
exercise, and various other changes may result owing to 
outside causes ; but as a result of these influences the 
animal is rarely so modified that one is unable to distinguish 
the species. Many of the sponges, however, are exceptions 
to this general rule. If, for example, some of the young 
of a certain parent develop in quiet water or in an un- 
favorable locality, they will usually be low, flat, and un- 
branched ; while the others, growing in swiftly running 
waterways, develop into tall, comparatively delicate and 
highly branched individuals. Under such circumstances 
not only does the external form become modified, but 
the internal organization may undergo profound change. 
The entire organism is plastic and readily molded by 
the influence of its surroundings, and the consequent 
lack of definite characters often renders it impossible 
3 



24 



ANIMAL FORMS 



to assign such forms to a definite position among the 

sponges. 

26. Structure of a simple sponge. — In the simpler sponges 

the body is usually vase-shaped (Fig. 13), with the base 

fastened to some foreign 
object, while at an oppo- 
site end an opening leads 
into a comparatively large 
internal cavity. This lat- 
ter space is also put in 
communication with the 
exterior by a multitude of 
minute pores which pene- 
trate the body wall. In 




Fig. 12.— Various forms of sponges, natural size. (From Nature.) 

the living condition currents of water continually pass 
through these smaller canals, and out of the large termi- 
nal opening, thus bringing within reach of the body minute 



THE SPONGES 



25 



floating organisms or organic remains which serve as food. 
The mechanism by which this process is effected, and the 
various other structures of the body, are in large part invis- 
ible from the exterior, requiring the 
study of thin sections of the sponge 
to make them clearly understood. 

Under the microscope such a sec- 
tion shows the body of a sponge to 
consist of an immense number of va- 
riously formed cells constituting three 
distinct layers (Fig. 14). Not only 
do these layers consist of different 
kinds of cells, but the duties per- 
formed by each are different. For ex- 
ample, a glance at Fig. 14 will show 
that in the inner layer certain colum- 
nar cells exist, provided with a fla- 
gellum and encircling collar, the ap- 
pearance being strikingly like certain 
of the Protozoa (Fig. 6, B). During 
life their whip-like processes, lashing 
backward and forward in perfect uni- 
son, produce currents of water which 
continually pass through the body. 
The food thus entering the animal is 
taken up by the cells of the inner 
layer as it passes by. The supply, 
however, is usually more than suffi- 
cient to meet the demands of this 
layer, and the excess is passed on to 
the middle and outer layers. The 
exact method by which this occurs is still a matter of 
doubt, but there seems to be little question but that 
each cell of the body receives its food in a practically un- 
modified condition, requiring that it digest as well as 
assimilate. The oxygen necessary to this latter process 




. 13.— One of the sim- 
plest sponges ( Calcolyn- 
thus primigenius (after 
Haeckel). A portion 
of the wall has been re- 
moved to show the in- 
side. 






26 



ANIMAL FORMS 




Fig. 14. — Portion of wall of sponge, showing three 
layers, e, outer layer ; i, inner layer, consisting 
of collared cells ; m, middle layer, consisting of 
irregular cells, among which are the radiate spic- 
ules and egg-cells. 



is absorbed by all parts of the body in contact with the 
water. 

27. Skeleton of sponges. — When it is remembered that 
the protoplasm composing the cells of the sponge has about 

the same consistence 
as the white of egg, 
it will be readily un- 
derstood why the 
greater number of 
sponges possess a skel- 
eton. Without such 
a support the larger 
globular or branched 
forms could not ex- 
ist, and even in the 
smaller members there would be danger of a collapse of the 
body walls and consequent stoppage of the food supply, 
owing to the closure of the pores. So in all but a very few 
thin or flat forms a skeleton appears in the young sponge 

almost before growth ....... ........... ^ .... 

has fairly begun, and ^N/£> ^^^ 

this increases with the 
body in size and com- 
plexity. It is formed 
by the activity of the 
cells of the middle layer, 
and may be composed 
either of a lime com- 
pound resembling mar- 
ble, or of flint, or of a 
horn-like substance resembling silk, or these may exist in 
combination in certain species. When consisting of either 
of the first-named substances it is never formed in one 
continuous piece, but of a vast multitude of variously shaped 
crystal-like bodies termed spicules (Fig. 15). These occur 
everywhere throughout the body, firmly bound together 




) 



Fig. 15.— Different types of sponge spicules. 




THE SPONGES 27 

by means of cells, or so interlocked that they form a rigid 
support to which the fleshy substance is bound and through 
which the numerous canals penetrate. 

In a relatively few species only does the skeleton con- 
sist of horn, though there are many in which horn and flint 
exist together. In the former event, if the skeleton be 
elastic and of sufficient size, it becomes valuable to others 
than the naturalist, for the familiar sponges of commerce 
are the horny skeletons of forms usually taken in the West 
Indies or in the Mediterranean Sea. In these localities the 
animals are pulled off by divers, or with hooks, and are then 
spread out in shallow water where the protoplasmic sub- 
stance rapidly decays. The remaining skeleton, thoroughly 
washed and dried, is ready for the markets of the civilized 
world. 

Examining a bit of such a " sponge " under a magnify- 
ing glass, it will be seen that the skeleton is not composed 
of various pieces, but of one continuous mass of branching 
fibers, which interlace and unite in apparently the greatest 
confusion ; yet in the living animal these were perfectly 
adapted to the position of the canals and the general needs 
of the animal. 

Besides being a scaffold-work to which the fleshy portions 
of the body are fastened, the skeleton serves also for pro- 
tection. In some species, needle-like spicules as fast as 
they are formed are partly pushed out over the entire sur- 
face of the body, giving the appearance of a spiny cactus ; 
or in other cases they are arranged in tufts about the canals, 
effectually preventing the entrance of any marauder. 
Thus perfectly protected, the sponges have but few natural 
enemies, and hence it is that in favorable localities they 
grow in great profusion. 

28. Race histories and life histories. — We have now traced 
living things from their simplest beginnings, where they 
exist as single cells, and have seen that in bygone times 
similar forms have united into simple colonies, and these 



28 ANIMAL FORMS 

through a division of labor among the constituent cells 
have resulted in Volvox-\ike colonies. There are the strong- 
est reasons for the belief that as these simple forms scat- 
tered into various surroundings and underwent changes to 
meet the shifting conditions, they assumed different de- 
grees of complexity that have resulted in the animal forms 
of the present day. 

It may have been noticed also that the sponge in its 
development passes through these stages : a single-celled 
egg ; later, a young form similar to Pandorina, then growing 
to look like Volvox, and finally assuming its permanent form. 
The history of the race of sponges and their development 
through a long line of ancestry of increasing complexity is 
thus told by the sponge as it develops from the egg into 
the adult ; and, so far as we know, all the many-celled ani- 
mals in their growth from the egg repeat more or less 
clearly the stages passed through by their forefathers. 



CHAPTER V 

THE CCELENTERATES 

29. General remarks. — This division of the many-celled 
animals includes the jelly-fishes, sea-anemones, and corals. 
A few species live in fresh water, but the majority are con- 
fined to the sea, being found everywhere from the shore- 
line and ocean surface to the most profound depths. 
Adapted to different surroundings and modes of life, they 
constitute a vast assemblage of the most bewildering di- 
versity. In some cases their resemblance to plants is re- 
markable, and the term zoophyte or " plant animal," occa- 
sionally applied to them, is the relic of former times when 
naturalists confounded them with plants. Even to-day 
certain species are sometimes collected and preserved as 
seaweeds by the uninformed. 

The general plan on which all coelenterates are con- 
structed is a simple sac, in some respects resembling that 
of the lower sponges, yet, since the modes of life of the 
members of the two groups are usually quite unlike, we 
shall find many profound differences between them. 

30. The fresh-water Hydra. — The bodily plan comes out 
most clearly in the Hydra (Fig. 16, A, D), which occurs 
upon the stems and leaves of submerged fresh-water plants 
in this and other countries. Its body, of a green or grayish 
color, according to the species, scarcely ever attains a diam- 
eter greater than that of an ordinary pin nor a length ex- 
ceeding half an inch. One end of the cylindrical organism 
is attached to some foreign object by means of a sticky 
secretion, but as occasion requires it may free itself, and by 

29 






30 



ANIMAL FORMS 



means of a " measuring-worm " movement travel to another 
place. 

Examined under a hand lens, the free end of the body 
will be found to support six to eight prolongations known 

as tentacles, which 
serve to convey 
food to the mouth, 
centrally located 
in their midst. 
This opening, un- 
like that of the 
sponges, is the 
only one leading 
directly into the 
large central gas- 
tric cavity which 
occupies nearly 
the entire animal 
(Fig. 16, D). As 
in the sponge, the 
cells of the body 
are arranged in 
the form of defi- 
nite layers, but the 
el} d \$^§p middle one is rep- 

resented only by 
a thin gelatinous 
sheet. 

31. Organs of 
defense. — These 
are the so-called 
lasso or nettle-cells 
(Fig. 16, C). Some 
of the cells of the outer layer possess, in addition to the 
elements of the typical cell, a relatively large spherical sac 
filled with a fluid, and also a spirally wound hollow thread 




Pig. 10.— The fresh-water Hydra. A, entire animal, de- 
veloping a new individual (enlarged 25 times). B. C, 
nettle-cells (after Scuneidek) ; D, section through 
the body. 






THE CCELENTERATES 31 

provided with barbs near its base. On the outer extremity 
of the nettle-cell projects a delicate bristle-like process, the 
trigger hair. These cells are especially abundant on the 
tentacles (Fig. 16, A, D), forming close, knob-like eleva- 
tions or " batteries," thus rendering it practically impossi- 
ble for any free-swimming organism to avoid touching them 
in brushing against the body. In such an event the dis- 
turbances conveyed through the trigger hair set up in some 
unknown way very rapid changes in the cell. This causes 
the sac to discharge the coiled thread and barbs into the 
body of the intruder, which is rendered helpless by the par- 
alyzing action of the fluid conveyed through the thread. 
Thus benumbed it is rapidly borne to the mouth and swal- 
lowed. In time new nettle-cells develop to take the place 
of those discharged and consequently worthless. 

32. Digestion of food. — Upon the interior of the body of 
Hydra and all of the ccelenterates the food, by reason of its 
large size, is incapable of being taken into the various cells. 
It is necessary, therefore, to break it up into smaller masses, 
and this is accomplished through the solvent action of the 
digestive fluid poured over it from some of the cells of the 
adjacent inner layer. When subdivided, the granules swept 
about the gastric cavity by the beating of the flagella (Fig. 
16, D) are seized by the processes on the free surfaces of the 
remaining inner layer cells, where they undergo the final 
stages of digestion ; then in a dissolved state they become 
absorbed and assimilated by all the cells of the body. 

33. Methods of multiplication. — Very frequently, espe- 
cially if the Hydra has been well fed, two or three pro- 
cesses arising as outpushings of the body wall may be 
noted upon the sides of the animal (Fig. 16, A, D). If 
these be watched from time to time they are found to in- 
crease in size, and finally, upon their free extremities, to 
develop a mouth and surrounding tentacles. Up to this 
point growth has taken place as a result of the assimilation 
of nutritive substances supplied from the parent ; but a con- 



32 



ANIMAL FORMS 




striction soon occurs which 
separates the young from the 
parent, and from that time 
on the two lead independent 
existences. At other times 
this asexual method of mul- 
tiplication is replaced by sex- 
ual reproduction, where new 
individuals arise from fertil- 
ized eggs. Both eggs and 
sperm arise in Hydra and in 
some other animals in the 
same individual, but in all 
such cases the eggs are fertil- 
ized by sperm which escape 
from some other individual. 
The fertilized egg, surround- 
ed by a firm coat, separates 
from the parent, drops to the 
bottom, and after a period of 
rest develops into a little Hy- 
dra which hatches and enters 
upon a free existence. 

Fig. 17.— Different types of Hydrozoan 
colonies. From Nature, the lower 
species magnified about 50 diameters. 



WW ) 



THE CCELENTERATES 33 

34. Hydrozoa, or Hydra-like animals. — Attention has al- 
ready been directed to the fact that the structure of Hydra 
is the simplest of the ccelenterates ; nevertheless, the thou- 
sand or more species belonging to this class which present 
a much more complicated appearance (Fig. 17) possess 
many fundamental Hydra-like characters. It is owing to 
this fact that this assemblage of forms has been placed in 
the class of the Hydrozoa, or Hydra-like animals. 

With but very few exceptions the members of this class 
are marine, usually living near the shore-line, where at 
times their plant-like bodies occur in the greatest profusion 
attached to rocks, seaweeds, or the bodies of other animals, 
particularly snails and crabs. Fig. 17 (upper colony) gives 
a good idea of one of the more complex forms, whose tree- 
like body attains in some cases the relatively giant height of 
from 15 to 25 cm. (six to ten inches). In early life it bears 
a close resemblance to a Hydra. Buds form in much the 
same way, but they retain permanently their connection with 
the parent, and in turn bear other buds, until finally the form 
shown in the figure is attained. In the meantime root-like 
processes have been forming which afford firm attachment 
to the object upon which the body rests. Also during this 
process the cells of the outer layer form a horny external 
skeleton ensheathing the entire organism except the ter- 
minal portions (the hydranths, Fig. 18, B) bearing the ten- 
tacles. The gastric cavities of all communicate, and the 
food captured by one ministers in part to its own needs 
and, swept through the tubular stalks and roots, is also 
shared by all other members. 

35. Jelly-fishes and the part they play. — During the pro- 
cess of growth a number of stubby branches arise which 
differ from the ordinary type in shape, and also in many 
casus as regards color. These club-like, fleshy portions de- 
velop close-set buds (Fig. 18, c) which early assume a bell- 
like shape, the point of attachment corresponding to the 
handle, while the clapper is represented by a short, slender 



34 



ANIMAL FORMS 



process bearing on its end an opening which becomes the 
mouth (Fig. 18, A). Around the margin of the bell nu- 
merous tentacles develop, and at the same time the gelati- 
nous substance situated between the outer and inner layers 
of the bell expands to a relatively enormous degree, giving 
it an increasing globular form and glassy appearance. 




Fig. 18.— A jelly-fish (Gonionemus), slightly enlarged. The stalked mouth is shown 
in dotted outline. B, C, enlarged portions of a hydroid colony bearing the 
mouth and tentacles ; j, a capsule within which the jelly-fish develop ; D, dia- 
gram of jelly-fish, illustrating its method of locomotion. 

Finally, vigorous movements rupture the connection with 
the parent, and this newly developed outgrowth, usually 
small, becomes an independent organism popularly termed 
a jelly-fish. While the external form of the jelly-fish appears 
to be widely different from the hydranths, a more careful 
study shows the difference to be superficial. Some zoolo- 
gists believe that jelly-fishes are simply buds which have 
become fitted to separate and swim away from the colony 
in order to distribute the young, as described hereafter. 
When the stalked colonies are very abundant the jelly- 



THE CGELENTERATES 35 

fishes may be liberated in such multitudes that the upper 
surface of the ocean for many miles may be closely packed 
with them in numbers reaching far into the millions. In 
these positions they are carried both by oceanic currents 
and through the alternate expansion and contraction of the 
bell, a movement resembling the partial closing and open- 
ing of an umbrella. In the jelly-fish the contraction is the 
more vigorous and rapid, and as it takes place the opening 
in the velum or veil (Fig. 18, i) is so narrowed that the water 
in the subumbrella space (a) is driven through it with con- 
siderable force, which results in driving the body in the 
opposite direction. 

The life of a jelly-fish is perhaps of short duration, last- 
ing not more than a few hours in some species, up to two 
or three weeks in others, but during that period they pro- 
duce multitudes of eggs which develop into minute free- 
swimming young. These settle down on some rock or sea- 
weed, and soon develop a Hydra-like body which, after the 
fashion described above, grows into another tree-like colony. 

36. Alternation of generations. — It will be noticed that 
the offspring of the jelly-fishes are not jelly-fishes, but stalked 
colonies, and these latter forms give rise to jelly-fishes. 
This is known as the alternation of generations, the jelly- 
fish generation alternating with the colonial form. This 
characteristic is of the greatest service in preventing the 
extermination of the race. Were the stalked forms to 
give rise directly to other stationary colonies, it is obvious 
that before long all the available space in the immediate 
locality would be filled. The food supply, always lim- 
ited, would not suffice, and starvation of some or imper- 
fect development of all would result ; but by means of the 
free-swimming jelly-fish new colonies are established over 
very extensive areas, and favorable situations are held 
by all. 

37. More complex types. — As mentioned above, there are 
perhaps upward of a thousand species of Hydrozoa, all with 



36 



ANIMAL FORMS 



essentially the same structure but with various modes of 
branching (for some of the commoner modes, see Fig. 17)- 
In some of the higher forms a division of labor has arisen 
among various members of the association which has led to 
most interesting results. For example, Fig. 19 represents 
a species of hydroid found investing the shells of sea-snails 
occupied by hermit crabs (Fig. 60). To the unaided eye 
its appearance is that of a delicate vegetable growth, but 
when placed under the microscope it is found to consist of 

a multitude of Hydra-like 
animals united by a hollow 
branching root system con- 
necting the gastric cavities 
of all of them (Fig. 19). 
Certain individuals (a) 
with tentacles and a mouth 
resemble a Hydra ; others, 
without a mouth and ten- 
tacles, are reduced to a 
. club-like form lb) liberally 

Fig. 19.— An enlarged portion of a hydroid t v ' J 

colony {Hydraclinia), showing (a) the supplied with nettle-Cells 

nutritive polyp, (b) the defensive polyp, U p 0n their free extremi- 

and (c) the reproductive polyp. . . 

ties; while the third type 
(c), likewise devoid of a mouth, possesses rudiments of ten- 
tacles below which are borne numerous clumps of repro- 
ductive cells. The first type, the only one possessing a 
mouth, captures the food, and after digesting it distributes 
the greater portion to the remaining members by means of 
the connecting root system ; those of the second form, de- 
fending the others by means of their nettle-cells against 
the inroads of a foreign enemy, are the soldiers of the colo- 
ny; while the third type produces the eggs from which 
new individuals develop. 

In some of the higher Hydrozoa, the Portuguese man- 
of-war (Fig. 20), this division of labor has reached a more 
advanced stage of development, and in addition the entire 




THE CCELENTERATES 



colony is fitted for a free-swimming existence. What cor- 
responds ordinarily to the attached stalk in other forms 
terminates in a bladder-like expansion, distended with 
gas, that serves as a float. From it are suspended individ- 
uals resembling great stream- 
ers sometimes many feet in 
length, without mouths, but 
loaded with nettle-cells that 
enable them to capture the 
food, which is conveyed to the 
second type, the nutritive 
polyps. Each of these is a 
simple tube bearing a mouth, 
and within them the food is 
digested and distributed by 
means of a branching gastric 
cavity extending throughout 
the entire colony. Then there 
are individuals like mouthless 
jelly-fishes which bear the 
eggs and care for the perpet- 
uation of the colony ; and be- 
sides these there may be some 
whose duty it is to defend the 
rest, and others whose active 
swimming movements, to- 
gether with the wind, drive 
the colony about. Thus uni- 
ted, sharing the food supply 
and working for the general welfare of all, the members of 
this colony live in greater security and with less effort than 
if, as separate individuals, each was fighting the battles of 
life alone. 

38. Scyphozoa. — The greater number of the larger and 
more conspicuous jelly-fishes are included under this term. 
In general shape and locomotion they resemble those of the 




Fig. 20. 



A colonial jelly-fi^h {Physalia). 
From Nature. 



38 



ANIMAL FORMS 



preceding group (Fig. 21), but, while the latter are generally 
very small, these forms are commonly from lour to twelve 
inches in diameter, and some measure one to two meters 
(three to six feet) across the bell. They are also distin- 
guished by means of tentacles which extend from the cor- 
ners of the mouth sometimes to a distance of several feet, 

and together with the 
marginal tentacles are 
formidable weapons for 
capturing small crabs, 
fishes, and other ani- 
mals which serve as 
food. In turn these 
forms serve as the food 
of many whales, por- 
poises, and numerous 
fishes which hunt them 
down, though the 
amount of nourishment 
they contain is prob- 
ably relatively small 
owing to the fact that 
in their composition 
there is a large percent- 
age of water (99 per 
cent in some species). The lobed margin of the bell, the 
absence of a definite swimming organ or velum, and the 
character of several of the internal organs, distinguish the 
larger from the smaller jelly-fish ; but the greatest differ- 
ence, however, is in the method of development. 

39. Development. — The eggs arise from the inner layer 
of the jelly-fish and drop into the gastric cavity, where each 
develops into a ciliated two-layered sac in some respects 
like that of a young sponge. Swimming away from the 
parent, they finally settle down, and attaching themselves 
(Fig. 22, a) assume the external form and habits of the sea- 




Fig. 21. 



-A jelly-fish {Rhizostoma), about one- 
fourth natural size. 



THE CCELENTERATES 



39 



anemones, described in the next section. In the course of 
time remarkable changes ensue, which first manifest them- 




Fig. 22.— Stages in the development of a scyphozoan jelly-fish, a, the attached 
young, which in b has separated into a number of disks, each of which becomes a 
jelly-fish, c. — After Korschelt and Heider. 

selves in a series of grooves encircling the body. These 
grow deeper, and the body of the animal finally comes to 
resemble a pile of sau- 
cers with the edge of 
each developed into a 
number of lobes (Fig. 
22, b). One after an- 
other each saucer, to 
preserve the simile, 
raises itself from the 
top of the pile and 
swims away, and is 
clearly seen to be a 
jelly-fish, though con- 
siderably unlike the 
adult. As growth pro- 
ceeds, however, it un- 
dergoes a series of transformations which result in the 
adult form. 




Fig. 23.— An attached scyphozoan jelly-fish 
(Haliclystus). Natural size, from Nature. 



40 



ANIMAL FORMS 



40. Sea-anemones. — In its external appearance the sea- 
anemone (Fig. 24) bears some resemblance to the Hydra, but 
is of a much larger size (1 to 45 cm., or ^ inch to 1-J- feet 
in diameter), and is frequently brilliantly colored. The 
number of tentacles is also more numerous, and the mouth 
leads into the body by means of a slender esophagus (Fig. 
25). Numerous partitions from the body wall extend in- 
ward, and many unite to the esophagus, keeping the latter 




24.— Sea anemones it he two upper figuresj and solitary coral polyi 



in position. Below the esophagus each partition projects 
into the great cavity of the body and bears upon its inner 
free edge several important structures. The first of these, 
known as the mesenteric filaments (Fig. 25), appearing like 
delicate frills, plays an active part in the digestion of the 
food. Associated with these are long, slender threads, 



THE CCELENTERATES 



41 



closely packed with innumerable lasso-cells, which may be 
thrown out through openings in the body wall when the 
animal is attacked. Lasso-cells are also very numerous on 
the tentacles, which are thus to some extent defensive, but 
are chiefly active in capturing the crabs and small fish 
which serve as food. 

The partitions also carry eggs which may undergo the 
first stages of their growth within the body, and when 
finally able to swim 
are sent out through 
the mouth opening 
by hundreds to seek 
out favorable situa- 
tions, there to set- 
tle down and re- 
main. In some spe- 
cies the young may 
sometimes arise as 
buds, as in Hydra 
(Fig. 24), and in 
others the animals 
have been described 
as splitting longi- 
tudinally into two 
equal-sized young. 

41. Corals.— The 
coral polyps also 

belong to this group, showing a very close resemblance to 
the sea-anemones. In most cases they develop a firm skel- 
eton of lime, commonly known as a coral/' which serves to 
protect and support the body. In a few species the polyps 
throughout life are solitary, and w r ith skeleton comparative- 
ly simple (Fig. 24) ; but the larger number of species be- 
come more complex by developing buds, which retain their 
connection with the parent, and in turn produce other out- 
growths with the ultimate result that highly branched 




Fig. 25.— Longitudinal section through the body of a 
sea-anernone. oe, esophagus ; m. /., mesenterial 
filaments ; r., reproductive organs. 



42 



ANIMAL FORMS 



colonies are produced (Fig. 26). At the same time the 
outer layer of the body is continually forming a skeleton 
which encloses the colony as a sheath, except at the ter- 
mination of each branch, where the mouth and tentacles 
are located. In certain species — for example, the sea pens 
{Pennatula) and sea fans (Gorgonia)—& skeleton may be 




I'k,. 86. - small portions of coral colonies, with some of the polyps expanded. 

formed of myriads of lime spicules, somewhat like those 
of the sponge, which are bound together by the fleshy 
substance of the body ; but the skeleton of most of the 
common forms in the ocean, and the coral found in 
general collections, is stony. According to their method 
of branching, such specimens have received various popu- 
lar names, such as brain, stag-horn, organ-pipe, and fun- 
gous corals. 



THE CGELENTERATES 43 

Nearly all species, like the sea-anemones, are brilliantly 
colored during life, and several are highly phosphorescent. 
All are marine, and while they are found everywhere, frem 
the shore-line to great depths, the more abundant and 
larger species inhabit the clear, warm waters of the tropics 
down to a depth of one hundred and sixty feet. In such 
regions the stag-horn corals especially grow in the wildest 
profusion, and become tall and greatly branched. Except 
in quiet water they are continually being broken by the 
waves, beaten into fragments, and the resulting sand is 
deposited about their bases. As a result of this continu- 
ous growth and erosion, there have been formed from coral 
sand mixed with the shells of mollusks and the skeletons 
of various Protozoa several of the islands along the Florida 
coast and many of those of the Pacific, some of them 
hundreds of miles in extent. 



CHAPTER VI 

THE WORMS 

42. General Characteristics.— The bodies of the animals 
comprising the two preceding groups are exposed on all 
sides equally to the water in which they live and are radi- 
ally symmetrical ; but in the worms, one side of the body 
is fitted for creeping, and for the first time we note a well- 
marked dorsal (back) and ventral (under) surface. In the 
former, the body, like a cylinder, may be divided into simi- 
lar halves by any number of planes passing lengthwise 
through the middle ; but in the worms, the right and left 
halves only are exposed equally to their surroundings, and 
there is, accordingly, only one plane which divides the body 
into corresponding halves, so that these animals, like all 
higher forms, are bilaterally symmetrical. In creeping, also, 
one end of the body is directed forward and it thus be- 
comes correspondingly modified. It usually bears the 
mouth, and may be provided with eyes, feelers, or organs 
of touch, and various other structures which enable the 
worm to recognize the nature of its surroundings. The 
nervous and muscular systems are better developed than in 
the foregoing groups, and we note a greater vigor and defi- 
niteness in the animal's movements, and in various ways the 
worms appear better able to avoid or ward off their enemies, 
recognize and select their food, and in general adapt them- 
selves to the conditions of life. 

The division of the worms is a very large one, and in 
some respects difficult to define, owing to the close resem- 
44 






THE WORMS 



blance which many of them show to animals in other 
groups. All the invertebrates, therefore, except the crabs 
and insects, were placed in one group until subsequent 
study made it possible to classify them more exactly. Ac- 
cording to the general shape of the body, and the arrange- 
ment of internal organs, worms are divided into a number 
of groups, chief among which are the flatworms, the thread 
or roundworms, and the ringed worms or annelids. 

The Flatworms 

•43. Form and habitat. — The flatworms, as their name 
indicates, are much flattened, leaf-like forms, some species 
living in damp places on land, 
in fresh - water streams or 
ponds, or along the seacoast, 
while a variety of other spe- 
cies are parasitic. The free 
forms (Fig. 27) are usually 
small, barely reaching a length 
greater than five or seven cen- 
timeters (2 to 3 inches), but 
some of the parasitic species 
(Fig. 31) attain the great 
length of six to thirteen me- 
ters (20 to 40 feet). 

The free-living forms usu- 
ally occur on the under side 
of stones, and frequently are 
so delicate that a touch is 
sufficient to destroy them. A 
few species are almost trans- fig. ot.-a, fresh-water flatworm {Ft* 

. , naria)', B, marine flatworm (Ia 

parent, while many are COl- plana) Enlarged, from Nature. 

ored to harmonize completely 

with their surroundings, so that, even though fragile and 
defenseless, they escape the attacks of enemies by being 
overlooked. The night-time or dark days are their hunting 




46 



ANIMAL FORMS 



season, and at such periods they maybe found moving about 
with a steady gliding motion (due to cilia covering the en- 
tire body), varied occasionally by a looping, caterpillar move- 
ment, or by swimming with a flapping of the sides of the 
body. When watched at such times they may sometimes 
be seen to snatch up small worms, snails, small crabs and 
insects, which serve as food. 

More closely examining one of these forms, for example, 
the species usually found on the under side of sticks and 
stones in our shallow fresh-water streams (Fig. 27, A), we note 
that the forward end is not developed into a well-defined 

head as in the higher worms, 
but is readily determined by 
the presence of very simple 
eyes and tentacles, while the 
lower creeping surface is dis- 
tinguished by a lighter color 
and the presence of the 
mouth. Through this small 
opening a slender proboscis 
(in reality the pharynx) may 
be extended some distance, 
and may be seen to hold the 
small organisms upon which 
it lives until they are suffi- 
ciently digested to be taken 
into the body. 

44, Digestive system. — In 
the smaller flatworms, some 
of which are scarcely larger 
than many of the Protozoa, 
the alimentary canal is a sim- 
ple unbranched tube ; but in 
the larger forms such an ap- 
paratus is replaced by a greatly branched digestive tract 
which furnishes an extensive surface for the rapid absorp- 



m 




Fig. 28.— Anatomy of fresh-water flat- 
worm {Planetaria), exs, excretory sys- 
tem, with flame-eel] (/). The ali- 
mentary canal is Stippled. I>. nerv- 
ous system. 



THE WORMS 



47 



tion of food, and extending deep into the tissues of the 
body, carries nutriment to otherwise isolated regions. In 
the fresh-water forms and their allies there are three main 
branches of the intestine (Fig. 28), while in many of those 
from the sea there are several, and their arrangement 
affords a basis for their general classification. 

45. Excretory system. — In the sponges and coelenterates 
the wastes are cast out by the various cells into the gastric 
cavity or at once to the exterior with- 
out the aid of any pronounced system 
of vessels ; but in the flatworms sev- 
eral of the organs are deeply buried 
within the tissues of the body and a 
drainage system becomes a necessity. 
This consists of a paired system of ves- 
sels extending the length of the ani- 
mal (Fig. 28) and provided with numer- 
ous branches, some of which open at 
various points on the surface of the 
body, while the others terminate in 
spaces (Fig. 29, s) among the organs in 
what are known as flame-cells. The 
substances which accumulate in these 
spaces are gathered up by the flame- 
cell, poured into the space it contains, and by means of the 
vibratory motion of its flagellum (/), a movement bearing 
a fancied resemblance to the flickering of a flame in the 
wind, are borne through the tubes to the exterior. 

46. Nervous system and sense-organs. — In the sponges no 
definite nervous system is known to exist, the slight move- 
ments which the cells are able to undergo being regulated 
somewhat as they are in the Protozoa. Among the coelen- 
terates certain of the cells scattered over the surface of the 
body are set aside as nerve-cells, and, more or less united by 
means of fibers extending from them, convey impulses over 
the body. In the flatworms the largernumber of nerve-cells 




Fig. 29. — Flame-cell of flat- 
worm (after Lang). /, 
flagellum ; n, nucleus; 
£, spaces among the or- 
gans of the body ; v, 
waste materials. 



48 ANIMAL FORMS 

are collected into two definite masses (Fig. 28, B), which 
constitute a simple brain on which the eyes are situated 
and from which bundles of nerve fibers pass to all parts of 
the body, the two extending backward being especially 
noticeable. As in the squirrel, these are distributed to the 
muscles and other organs to regulate their activity, while 
those distributed to the skin, especially in the forward 
part of the body, convey stimuli produced by touch. The 
branches connecting with the eyes enable the animal to 
distinguish light from darkness, but are probably too sim- 
ple to allow it to clearly distinguish objects of the outside 
world. The sense of smell and possibly that of taste are 
also present, but are relatively feeble. 

Some other characters of this class will be noted in the 
consideration of the two following classes. 

47. Parasitic flatworms (trematodes) — parasitism. — Men- 
tion has already been made of the associations of two ani- 
mals as " messmates " for mutual benefit, such as the Hy- 
dractinia growing on the surface of the shell inhabited by 
the hermit crab, to which it gives protection by means of 
its nettle-cells, while in turn being borne continually into 
regions abounding with food. More frequently, however, 
one animal derives benefit from another without making 
any compensation. For example, many species of flatworms 
live within the shells of certain snails and upon the bodies 
of sea-urchins and starfishes, where they gather in their 
food supply safe from the attacks of enemies. Such asso- 
ciations are probably without much if any inconvenience to 
the animal thus inhabited, and it also appears probable 
that the tenants are transients, using the mollusk or star- 
fish only as a temporary home. But from this condition of 
affairs it is only a short step to the parasitic habit, where 
the association becomes permanent and the occupant is 
provided with various structures which prevent its sepa- 
ration from its host. This latter kind of union occurs 
throughout the group of trematodes; all are parasitic, and 



THE WORMS 



49 



their internal organization, so closely resembling that of 
the free-living forms as to need no further description, in- 
dicates that they are 
descendants of the lat- 
ter. In the greater 
number the body is 
flat, and a few species 
still retain their outer 
coat of cilia ; but since 
these are no longer of 
service as locomotor 
organs they have gen- 
erally disappeared, and 
in their place numer- 
ous adhesive organs, 
such as spines, hooks, 
and suckers (Fig. 30), 
have arisen, which en- 
able the animals to 
hold on with great te- 
nacity. Thus attached 
to its host, and using 
it as a convenient and 
comparatively safe 
means of locomotion, 
the parasite may still 

continue to capture small animals for food or may derive 
its nourishment from the tissues of the host. In addition 
there are numbers of internal parasites, living almost ex- 
clusively in the bodies of vertebrate animals, scarcely a sin- 
gle one escaping their ravages. 

48. Life history. — In the external parasites the young 
hatch out and with comparative ease make their way to 
another host ; but the young of an internal parasite, inhab- 
iting the alimentary canal, have a very slight chance in- 
deed of ever reaching a similar location in another host. 




Fig. 30. — A parasitic flatworm {Ejnciella). m 
mouth ; o, opening of reproductive system ; 
s, sucker and spines for attachment. The di- 
gestive system is stippled ; nervous system 
black. Enlarged 8 times, from Nature. 



50 ANIMAL FORMS 

For this reason an almost incredible number of eggs is laid, 
and some extraordinary measures are employed in effecting 
the desired result. Probably the best-known example is that 
of the liver fluke inhabiting the bile-ducts in the sheep. 
Each worm lays several hundred thousand eggs, which make 
their way from the host, and if they chance to fall in pools 
of water or damp situations may proceed to develop, other- 
wise not. If the surroundings be favorable, the young, like 
little ciliated Infusoria, escape from their shells and rest- 
lessly swim or move about for a short time, and if during 
this time they come in contact with certain species of 
snails living in these situations they at once bore into their 
bodies. Here they produce other young somewhat resem- 
bling a tadpole, that now make their escape from the snail. 
In a short time each one crawls upon a blade of grass, and 
surrounds itself with a tough shell, where it may remain for 
several weeks. If the grass on which they rest be eaten by 
a sheep, they finally make their way to the bile-ducts and 
there become adult. The life cycle is now complete ; the 
young form has found a new host ; and the process shows 
how wonderfully animals are adapted to the conditions which 
surround them, and how closely they must conform to these 
conditions in order to exist. 

49. The tapeworms (cestodes). — The cestodes, or tape- 
worms, are also parasitic flatworms in which the effects of 
such a mode of life are strongly marked. They occur 
almost exclusively in the bodies of vertebrate hosts and 
exhibit a great variety of bodily forms, in some cases resem- 
bling rather closely the trematodes, but in others strikingly 
different. In the latter type the body is usually of great 
length (from a few centimeters to upwards of sixteen meters 
(50 feet) ), and terminates in a "head " (Fig. 31) provided, 
in the different species, with a great variety of hooks and 
spines and numbers of suckers for its attachment to the 
body of the host. From the head the body extends back- 
ward in the gradually enlarging ribbon-like body, slender at 



THE WOK MS 




first and scarcely showing the segments which finally be- 
come so prominent a feature. 

When carefully examined, a two-lobed brain is found 
in the "head," and from it nerves extend the entire length 
of the body, followed throughout their 
course by the tubes of the excretory 
system ; also each segment contains a 
perfect reproductive system, so that 
even if it be separated from the others 
it may continue to exist for a consid- 
erable length of time. Furthermore, 
the tapeworms are surrounded by the 
predigested fluids of their host ; a 
special alimentary canal is therefore 
superfluous, and all traces of it have 
disappeared. 

50. Development. — As the animal 
clings in this passive way to the body 

Of itS host the Segments, loaded with Fig. 31.— Tapeworm (Tamia 
-1 p -, -1 solium). In upper left- 

eggs ready for development, separate hand c ; orner of ^ gure i8 
one after another from the free end the much enlarged head, 
of the body, pass to the exterior, and 

slowly crawling about like independent organisms, lay great 
numbers of eggs, which may find an intermediate host as in 
the life cycle of the liver fluke, and so in time find their 
permanent resting-place. Fortunately in all these parasitic 
forms, though an inconceivably great number of eggs are 
laid, only a comparatively few reach maturity. Even these, 
however, may cause at times great destruction among the 
higher, and especially our domestic, animals, often doing 
damage amounting to many millions of dollars per year. 

51. The tapeworm in relation to regeneration. — It lias 
been known for more than one hundred and fifty years that 
some of the lower animals possess to a surprising degree 
the ability to regenerate parts of the body lost through 
injury. The Hydra, hydroids, and some of the jelly-fishes 




52 ANIMAL FORMS 

may be cut into a number of pieces, each of which will 
develop into a complete individual ; and this power of recov- 
ery from the injuries produced by enemies is of the great- 
est service in the perpetuation of the species. This ability 
is also present in certain flatworms, and some species are 
known which voluntarily separate the body into two por- 
tions, each of which becomes an adult. In other species a 
similar process results in the formation of a chain of six 
individuals, placed end to end, the chain finally breaking 
up into as many complete worms. It is possible that the 
tapeworm may also be looked upon as a great chain of 
united individuals produced by the division of a single 
original parent, which becomes adapted for attaching the 
others until they separate. These latter are capable only of 
a very sluggish movement, and, devoid of mouth and ali- 
mentary canal, are not able to digest their food, but their 
life work is to so lay their eggs that they may develop into 
other individuals, and for this they are well adapted. 

Nematodes (Threadworms) 

52. General characters. — This class of worms is com- 
posed of an enormous number of different species, some para- 
sitic, others free all or a portion of their lives, and in view of 
the fact that they inhabit the most diverse situations it is 
remarkable that they are so uniform in their structure. In 
all the body is slender, and the general features of its organ- 
ization may be readily understood from an examination of 
the " vinegar eel" (Fig. 32, A). This small worm (not an 
eel), a millimeter or two in length, lives on the various forms 
of mold that grow in fermenting fruit juices, especially 
after a little sugar or paste has been added. A tough cuti- 
cle surrounds the body, preserving its shape and at the 
same time protecting the delicate organs against the act ion 
of the acids in which it lives. Through this may be seen 
great bands of muscles extending the entire length of the 
body and producing the wriggling movements of swimming 



THE WORMS 



5:; 



or crawling. The) T also give support to a brain, which is in 
the form of a collar encircling the pharynx near the head, 
and to the great nerves which extend from it. Still fur- 
ther within the transparent body the alimentary canal may 
be distinguished as a straight tube 
passing directly through the ani- 
mal. This latter system lies freely 
in a great space, the body cavity, 
traces of which may exist in the 
flatworms in the form of small hol- 
lows among the organs into which 
the kidneys open. It is possible 
that in this form also the kidneys 
open into this space, and it is 
roomy enough besides to afford 
lodgment for the reproductive or- 
gans in addition to a large amount 
of fluid which is probably somewhat 
of the nature of blood. A space in 
some respects similar to this occurs 
in all the animals above this group, 
and as we shall see, it is often cu- 
riously modified and serves for a 
number of different and highly im- 
portant purposes. In the round- 
worms the fluid it contains proba- 
bly acts in the nature of a blood 
system, distributing the food and 
oxygen to various parts of the body and carrying the wastes 
to the kidneys for removal. 

53. Multiplication. — In the matter of the production of 
new individuals the greatest differences exist. In some 
threadworms, for example the "vinegar eel," eggs develop 
within the body and the young are born with the form of the 
parent. In other cases the eggs are laid in the water, where 
they, too, may directly grow to the adult condition ; but in 




Fig. 32. — Thread- or round- 
worms. A, vinegar eel (An- 
guillula) ; m. mouth ; ph., 
pharynx ; i, intestine ; ov. t 
developing young. B. Tri- 
china. From Nature, greatly 
enlarged. 



54: ANIMAL FORMS 

the greater number of species the development is round- 
about, and one or more hosts are inhabited before the young 
assume the adult condition. Such is the case with the 
dreaded Trichina (Fig. 32, B), which infests the bodies of 
several animals, particularly the rat. When these forms 
are introduced into the alimentary canal of the rat, for 
example, they soon lay a vast quantity of eggs, sometimes 
many millions, which develop into young that bore their 
way into the muscles of the body, where they may remain 
coiled up for years. If the body of the rat be eaten by some 
carnivorous animal, these excessively small young are lib- 
erated during the process of digestion and rapidly assume 
the adult condition in the alimentary canal, likewise giving 
rise to young which pursue again this same course of 
development. 

Another example of a complicated life history is in 
the Gordius or " horsehair snake " (a true worm and not a 
snake) frequently seen in the spring in pools where it lays 
its eggs. These eggs develop into young which bore their 
way into different insect larvae, which are in turn eaten by 
some spider or beetle, and the worm thus transferred to a 
new host. In this they grow to a considerable size, and 
then make their exit from the body of the host and finally 
become adult. 

54. Spontaneous generation. — It is only within compara- 
tively recent years that such life histories have been under- 
stood. Formerly the sudden appearance of these and other 
forms in various situations were accounted for on the ground 
that they arose spontaneously without the intervention of 
any living creature. Even yet we hear of the transforma- 
tion of horsehairs into hairworms, and of frogs, earthworms, 
and several other animals from inorganic matter, but such 
assertions are based on superficial observations, and at the 
present time no exception is known to the law that living 
creatures arise from preexisting living parents. "All life 
from life " (omnium vivum ex vivo) is a universal law. 



THE WORMS 

Annelids or Segmented Worms 

55. The earthworms and their relatives. — Leaving the 
groups of the parasitic animals, which have been driven from 
the field of active existence and in many ways are degraded 
by such a mode of life, we pass on to the higher free-living 
worms, where brilliant colors, peculiar habits, or remarkable 
adaptations render them peculiarly interesting. In consid- 
ering first their general organization, we may use the earth- 

C 

in 

Fig. 33.— Earthworm (Lumbricus terrestris). ra, mouth ; c, girdle or clitollum. 

worm (Fig. 33) (sometimes called angle-worm or fish-worm) 
as a type because of its almost universal distribution. 

The body is cylindrical, shows well-marked dorsal and 
ventral surfaces, and, as in all of the annelids, is jointed, 
each joint being known as a segment. Anteriorly it tapers 
to a point, and the head region bearing the mouth is ill- 
defined, unlike many sea forms, yet serves admirably for 
tunneling the soil in which all earthworms live. In this 
process the animal is also aided by bristles or setce which 
project from the body wall of almost every segment and 
may be stuck into the earth to afford a foothold. 

56. Food and digestive system. — The earthworms are 
nocturnal animals, seldom coming to the surface during the 
day except when forced to do so by the filling of their tun- 
nels with water or when pursued by enemies. At night 
they usually emerge partially, keeping the posterior end of 
the body within the burrow, and thus they scour the sur- 
rounding areas for food, which they appear, in some cases 
at least, to locate by a feeble sense of smell. They also 
frequently extend their habitations, and in so doing swallow 
enormous quantities of earth from which they digest out 
any nutritive substances, leaving the indigestible matter in 

5 



50 



ANIMAL FORMS 



coiled " castings " at the entrance of the burrows. In thus 
mixing the soil and rendering it porous they are of great 
service to the agriculturist. 

Although earthworms are omnivorous they also manifest 
a preference for certain kinds of food, notably cabbage, 
celery, and meat, which leads us to think that they have a 
sense of taste. All these substances are carried within their 
retreats and devoured, or are used to block the entrance 
during the day. The food thus carried within the body is 
digested by a system (Fig. 34) composed of several portions, 




_ v-vr 

yi C. K si' o id. id 

Fig. 34.— Earthworm (Lvmbricus) dissected from left side, b, brain; c, crop; d, 
outer opening of male reproductive system ; dv, dorsal blood-vessel ; g, gizzard : 
h, pulsating vessels or " hearts " ; z, intestine ; k, kidney ; m, mouth ; n. c, nerve- 
cord ; oe, esophagus ; o, ovary ; od, oviduct ; p7i, pharynx ; r, testes ; s.r., sem- 
inal receptacles ; v. v., ventral vessel. 

each of which is modified for a particular part in the pro- 
cess. The mouth (m) leads into a muscular pharynx {j)h) 
whose action enables the worm to retain its hold on various 
objects until swallowed, and this in turn is continuous with 
the esophagus. From here the food is passed into the thin- 
walled crop (c),and from this storehouse is gradually borne 
into the gizzard (#), whose muscular walls reduce it to a fine 
pulp now readily acted upon by the digestive fluids. These, 
resembling in their action the pancreatic juice of higher 
animals, are poured out from the walls of the intestine into 
which the food now makes its way; and as it courses down 
this relatively simple tube the nutritive substances are ab- 
sorbed while the indigestible matters are cast away. 

57. Circulatory system. — In all the groups of animals up 
to this point the digested food is carried over the body by 
a simple process of absorption, or in the threadworms by 



THE WORMS 



57 



means of the fluid in the body cavity ; but in the earthworm 
the division of labor between different parts of the body is 
more perfect, and a definite blood system now acts as a 
distributing apparatus. This consists primarily of a dorsal 
vessel lying along the dorsal surface of the alimentary ('anal 
(Fig. 34), from which numerous branches are given off to 
the body wall, and to the digestive system through which 
they ramify in every direction before again being collected 
into a ventral vessel lying below the digestive tract. In 
some of the anterior segments a few of the connecting 
vessels are muscular and unbranched, and during life pul- 
sate like so many hearts to force the blood over the body, 
forward in the dorsal vessel, through the " hearts " into the 
ventral vessel, thence into the dorsal by 
means of the small connecting branches. 

Some of the duties of this vascular 
system are also shared by the fluid of 
the body cavity, which is made to cir- 
culate through openings in the parti- 
tions by the contractions of the body 
wall of the animal in the act of crawl- 
ing. In this rough fashion a consider- 
able amount of nutritive material and 
oxygen are distributed to various or- 
gans, and wastes are carried to the kid- 
neys to be removed. 

58. Excretion. — In nearly all of the 




segmented worms there is a pair of 



Fig. 85.— Diagram of earth- 
worm kidney. 6, blood- 
vessel ; /, funnel open- 
ing into body cavity ; 
o, outer opening ; s, 
septum ; u\ body wall. 



kidneys to every segment (Figs. 34, 35). 
Each consists of a coiled tube wrapped in a mass of small 
blood-vessels, and at its inner end communicating with the 
body cavity by means of a funnel-shaped opening. In 
some unknown way the walls of the kidney extract the 
waste materials from the blood-vessels coursing over it and 
pass them into its tubular cavity. At the same time the 
cilia about the mouth of the funnel-shaped extremity are 



58 ANIMAL FORMS 

driving a current from the body-cavity fluids, which wash 
the wastes to the exterior. 

59. Nervous system. — The nervous system of the earth- 
worm consists first of a brain composed of two pear-shaped 
masses united together above the pharynx (one shown in 
Fig. 34), from which nerves pass out to the upper lip and 
the head, which are thus rendered highly sensitive. Two 
other nerves also pass out from the brain, and, coursing 
down on each side of the pharynx like a collar, unite below 
it and extend side by side along the under surface of the 
digestive system throughout its entire extent. In each 
segment the two halves of this ventral nerve-cord are united 
by a nerve, and others are distributed to various organs, 
which are thus made to act and in proper amount for the 
good of the body as a whole. 

In its relation to the outside world the chief source of 
information comes to the earthworm through the sense of 
touch, for definite organs of sights taste, and smell are but 
feebly developed, while ears appear to be entirely absent. 
Nevertheless these are sufficient to enable it to lead a suc- 
cessful life, as is evidenced by the great number of such 
forms found on every hand. 

60. Egg-laying. — In digging up the soil where earth- 
worms abound one frequently finds small yellowish or 
brownish bodies looking something like a grain of wheat. 
These are the cocoons in which the earthworms lay their 
eggs, and the method by which this is performed is unique. 
We have already noted the presence of a swollen girdle 
(the clitellum) about the body of the worm. At the breed- 
ing season this throws out a fluid which soon hardens into 
an encircling band. By vigorous contractions of the body 
this horn-like collar is now slipped forward, and as it passes 
the openings of the reproductive organs the eggs and 
sperms are pushed within it. They thus occupy the space 
between the worm and the collar, and when the latter is 
shoved off over the head its ends close as though drawn to- 



THE WOK MS 



59 



gether by elastic bands. A sac, the cocoon, is thus pro- 
duced, containing the eggs and a milky, nutritive substance. 
In a few weeks the worm 
develops and, bursting the 
wall of its prison, makes its 
escape. * 

61. Distribution. — The 
earthworms and their allies 
are found widely distributed 
throughout the world, and 
all exhibit many of the 
characters just described. 
The greatest differences 
arise in their mode of life : 
some are truly earthworms, 
but others are fitted for a 
purely aquatic existence in 
fresh water or along the 
seacoast ; a few have taken 
up abodes in various ani- 
mals and plants, and in 
some of these situations they 
extend far up the sides of 
the higher mountains. In 
all, the head is relatively 
indistinct, the number of 

bristles 011 each segment Fig. 36.-A marine worm (Nereis). A ap- 
° pearance at breeding season, and B, 

few, and for this and other at ()ther times . 

reasons all are included in 

the subclass Oligochaete, or " few-bristle " worms. 

62. Nereis and its allies.— In many of the above-men- 
tioned situations members of a more extensive group of 
worms are found, with highly developed heads and many 
bristles arranged along the sides of the body. These are 
the Polychsetes or " many-bristle " worms, and as a repre- 
sentative we may take Nereis (Fig. 36), a very common 




60 



ANIMAL FORMS 



form along almost any seashore. The body presents the 
same segmented appearance as the earthworm, but the 
head (Fig. 37, A) is provided with numerous sense organs, 
chief among which are four eyes and 
several tentacles or " feelers." 

The segments behind the head 




Fig. 37.— A, head and one of the lateral appendages (B) of a marine worm (Nereis 
brandtn) ; aL intestine ; /, " gill " ; k, kidney ; n, nerve cord ; s, bristles for loco- 
motion. 

differ very little from one another, and, unlike those of 
the earthworm, each bears a pair of lateral plates (Figs. 
36, 37, B) or paddles with many lobes, some of which bear 
numerous bristles. By a to-and-f ro movement these organs 
aid in pushing the animal about, or may enable certain spe- 
cies to swim with considerable rapidity. 

As in all other worms, respiration takes place through 
the surface of the body, the area of which is increased by 
the development, on certain portions of the paddles (para- 
podia), of plates penetrated with numerous blood-vessels, 
which thus become special respiratory organs or gills 
(Fig. 37, B). 

In their internal organization the Polychaetes are con- 
structed practically on the same plan as the earthworms, 
the principal difference being in the reproductive system. 
In the earthworm this is restricted to sonic of the forward 
segments, while in the present group the eggs and sperms 



THE WORMS 



61 



$M$fa 



are developed in almost every segment, whence they are 
finally swept to the exterior through the tubes of the kid- 
neys (Fig. 37, 13). 

The Nereis and its immediate relatives are all active 
forms, and by means of powerful jaws, which may be quickly 
extended from the lower part of the mouth cavity, they 
capture large numbers of small crustaceans, mollusks, and 
worms which happen in their path. Others more distantly 
related make their diet of seaweed, and 
many living on the sea bottom swallow 
great quantities of sand, from which they 
absorb the nutritious substances. 

63. Sedentary forms. — Preyed upon by 
many enemies, a large number of species 
have been forced to abandon an active ex- 
istence save in their early youth, and to 
construct many interesting devices for their 
protection. Numerous species, shortly after 
they commence to shift for themselves? 
build about their bodies tubes of lime (Fig. 
39), from which they may emerge to gather 
food and into which they may dash in times 
of danger. As the worm grows the tube is 
correspondingly enlarged, and these tubes, 
in all stages of construction and variously 
coiled, may be found on almost every avail- 
able spot at the seashore, and may often 
be seen on the shells of oysters in the 
markets. 

In other species the tube is like thin 
horn, and may be further strengthened or 
concealed by numerous pebbles, bits of carefully selected 
seaweeds, or highly tinted shells, which give them a very 
attractive appearance. Such species usually develop out 
of immediate contact with other forms, but a few live 
so closely associated together that their twisted tubes 




Fig. 38.— A common 
marine worm ( Po- 
ly nee brevisetosa), 
with extended pro- 
boscis and over- 
lapping plates cov- 
ering the back. 



62 



ANIMAL FORMS 



form great stony masses, sometimes several feet in dia- 
meter. 

64. Effects of an inactive life. — In many species such a 
sedentary life has resulted in the almost complete disap- 
pearance of the lateral appendages, which therefore no 
longer serve as organs of respiration, and this function has 
been shifted accordingly on to other structures. These 
new organs are situated principally on the exposed head, 




Fig. 39.— Sedentary tube-dwelling marine worms, upper left hand Sabella (one-half 
natural size), the remainder Serpula (enlarged twice). From life. 

and Fig. 39 shows the general appearance of some com- 
mon species. The corners of the mouth have expanded 
into great plumes, sometimes wondrously colored like a 
full-blown flower, and these, bounteously supplied with 
blood-vessels, act as gills. When disturbed, the plumes are 
hastily withdrawn into the tube, and some of the so-called 
serpulids (Fig. 30, bottom of figure) close the entrance with 
a funnel-shaped stopper. While the plumes are primarily 
respiratory organs, they also act as delicate feelers, and may 
even bear a score or more of eyes ; and in addition, being 



THE WORMS 



63 




covered with cilia, create the currents of water which 
bring minute organisms serving as food within reach of 
the mouth. 

05. Development. — Unlike the earthworms, the Poly- 
chsetes lay their eggs in the sea water, where they are left 
alone to develop as best they may. Both the male and 
female Nereis, as the egg-laying time approaches, undergo 
remarkable changes in their external appearance, resulting 
in the form shown in Fig. 36, A. 
They are now active swimmers, and 
thus are able to scatter the fertilized 
eggs over wide and more or less favor- 
able areas. The young also for a 
time are free-swimming, but finally 
end their migrations by settling to 
the sea bottom, where they gradually 
attain the adult condition. 

As in some of the flat worms, re- 
production may also arise asexually 
by the division of the animal into two 
or more parts, each of which subse- 
quently becomes a complete indi- 
vidual. In other species growth of 
various parts may result in two com- 
plete worms at the time of separation ; 
and from such forms we may trace a 
fairly complete series up to those in 
which the original parent breaks up 
into twenty to thirty young. 

66. The leeches. — At first sight 
the leeches (Fig. 40), or at least the 
smaller, more leaf-like forms, might 

be mistaken for flat worms, especially for some of the para- 
sitic species. As in the latter, the mouth is surrQunded by 
a sucker, and another is located at the hinder end of the 
body, but beyond this point the resemblance ceases. The 




VI 

Fig. 40.— A leech {Maerobdel- 
la). Right-hand figure il- 
lustrates alimentary canal. 
ph, pharynx ; c. crop ; p, 
lateral pouches ; s.i., in- 
testine. 



64 ANIMAL FORMS 

outer surface is delicately marked off into eighty or a hun- 
dred rings, of which from three to five are included in one 
of the deeper true segments corresponding to those of 
other annelids. From two to ten pairs of simple eyes are 
borne on the head, and owing to the fact that they are 
active swimmers, or move by caterpillar-like looping, loco- 
motor spines are unnecessary and absent. In their internal 
organization, however, there are many features which in- 
dicate a close relationship with the Oligochaetes or few- 
bristle worms. The nervous, circulatory, and certain char- 
acteristics of the excretory systems are decidedly similar, 
but, on the other hand, some facts are difficult to explain 
on such a theory, and have led some zoologists to the belief 
that the relationship of these animals can not at present 
be determined. 

67. Haunts and habits. — The leeches usually dwell in 
among the plants in slowly running streams, but some 
occur in moist haunts on land, and a considerable number 
live in the sea. All are " bloodsuckers " — fierce carnivo- 
rous worms, whose bite is so insidiously made that the vic- 
tim frequently is ignorant of their presence. Fishes, frogs, 
and turtles are the most frequently attacked, but cattle and 
other animals which come down to drink also become their 
prey. In some of the tropical countries the land-leeches 
are present in large numbers secreted among the leaves, and 
so severe are their attacks that various animals, even man, 
succumb to their united efforts. Adhering by their suck- 
ers, they puncture the skin, some using triple jaws, and 
fill themselves until they become greatly distended, when 
they usually drop off and digest the meal at leisure. In 
certain species the intestine is provided with lateral 
pouches (Fig. 40), which serve to store up the food until 
the time for digestion arrives. A full meal is sufficient 
with some species to last for two or three months, and the 
medicinal or horse-leech when gorged with food may con- 
sume a year in digesting it. 



THE WORMS 65 

68. Egg-laying. — The eggs of some leeches are stored 
up in a cocoon like that of the earthworm, which is attached 
to submerged plants or placed under stones. When fcho 
young are able to lead independent lives they emerge with 
the form of the parent. A leaf-like form, Clepsine^ some- 
times found adhering to turtles, fastens the eggs to the 
under side • of its body, and the young when hatched 
remain there for several days, adhering by their posterior 
suckers, 



CHAPTER VII 



ANIMALS OF UNCERTAIN RELATIONSHIPS 



In this chapter we shall consider in a brief way a number 
of different groups of animals whose relationships are un- 
certain. Up to the present time the study of their habits, 
structure, and development has been of too fragmentary 
or unrelated a character to enable the majority of zoologists 
to agree upon their classification. Nevertheless, many of 
them are highly interesting and attractive, 
often very common, and in some respects 
they hold important positions in the animal 
kingdom. 

69. The rotifers or wheel-animalcules. — 
The rotifers or wheel-animalcules are rela- 
tively small and beautiful organisms, rarely 
ever longer than a third of an inch, but at 
times so abundant that they may impart a 
reddish tinge to the water of the streams 
and ponds in which they live. At first 
sight they might be mistaken for one-celled 
animals, but the presence of a digestive 
tract and of reproductive elements soon dis- 
pels such a belief. Examined under the 
microscope, the more common forms are 
seen to possess an elongated body terminat- 
at the forward end in two disk-like expansions beset 
along the edges with powerful cilia. These serve to drive 
the animal about, or, when it remains temporarily attached 
66 




Fig. 41.— A wheel- 
animalcule (Rotifer) 



mi 



ANIMALS OF UNCERTAIN RELATIONSHIPS 67 

by the sticky secretion of the foot, to sweep the food-par- 
ticles down into the mouth. Through the walls of the 
transparent body such substances are seen to pass into the 
stomach, where they are rapidly hammered or rasped into 
a pulp by the action of several teeth located there. In 
the absence of a circulatory system the absorbed food is 
conveyed by the fluid of the body-cavity, which also con- 
veys the wastes to the delicate kidneys. Several other 
features of their organization are of much interest, espe- 
cially to the zoologist, who believes that he gains from 
their simple structure some ideas of the ancestors of the 
modern worms, mollusks, and their allies. During the 
summer the rotifers lay two sizes of " summer eggs," 
which are remarkable for developing without fertilization. 
The large size give rise to females, the smaller to males, the 
latter appearing when the conditions commence to be un- 
favorable. The " w r inter eggs," fertilized by the males and 
covered with a firm shell, are able for prolonged periods to 
withstand freezing, drought, or transportation by the wind. 
The adults also are able under the same adverse conditions 
to surround themselves with a firm protective membrane 
and to exist for at least a year. Once again in the presence 
of moisture the shell dissolves, and in a surprisingly short 
space of time they emerge, apparently none the worse for 
the prolonged period of quiescence. 

70. Gephyrea. — There is a comparatively large group of 
worm-like organisms, over one hundred species in all, which 
at present hold a rather unsettled position in the animal 
kingdom. Some of the more common forms (Fig. 42) 
living in the cracks of rocks or buried in the sand, usually 
in shallow tide pools along the seashore, have a spindle- 
shaped body terminated at one end by a circlet of tentacles 
which surround the mouth. On account of their external 
resemblance to many of the sea-cucumbers (Fig. 92), they 
were earlier associated in the same group ; but an examina- 
tion of their internal organization inclines many zoologists 



68 



ANIMAL FORMS 



U.C. 



m 



to the belief that the ancestors of some of these animals 
were segmented worms whose present condition has arisen 
possibly in accordance with their sluggish habits. This 
view is strengthened by the fact that in a very few species 

the larvae are dis- 
tinctly segmented, 
but lose this char- 
acter in becoming 
adult. As before 
mentioned, the 
greater number of 
species live in bur- 
rows in the sand 
or crevices in the 
rocks, from which 
they reach out and 
gather in large 
quantities of sand. 
As these substances 

Fig. 42.— A gephyrean worm (Dendrostoma) . Specimen pass down the in- 
on left opened to show Jc, kidney, m, muscle bands, . i • . i , • 

and n.c. t nerve-cord. testme the nutn ' 

. tive matters are di- 
gested and absorbed, while the indigestible matters are 
voided to the exterior. When large numbers are associated 
together they are doubtless important agents in modifying 
the character of the sea bottom, thus acting like the earth- 
worms and their relatives. 

71. The sea-mats (Polyzoa). — The sea-mats or Polyzoa 
constitute a very extensive group of animals common on 
the rocks and plants along the seashore, and frequently 
seen in similar situations in fresh-water streams. A few 
lead lives as solitary individuals, but in the greater number 
of species the original single animal branches many times, 
giving rise to extensive colonies. In some species these 
extend as low encrusting sheets over the objects on which 
they rest ; while in others the branches extend into the 





ANIMALS OF UNCERTAIN RELATIONSHIPS 



69 



surrounding medium and assume feathery shapes (Fig. 43), 
which often bear so close a resemblance to certain plants 




Fig. 43.— Lamp-shells or Brachiopods (on left of figure), fossil and living, and t,on 
right) plant-like colonies of sea-mats. 

that they are frequently preserved as such. What their 
exact position is in the animal scale it is somewhat difficult 
to say ; but judging especially from their development, it 
appears probable that they are distant relatives of the seg- 
mented worms. 



TO ANIMAL FORMS 

72. Lamp-shells or Brachiopods. — Occasionally one may 
find cast on the beach or entangled in the fishermen's 
lines or nets a curious bivalve animal similar to the form 
shown in Fig. 43. These are the Brachiopods, or lamp- 
shells. The remains of closely related forms are often 
abundant as fossils in the rocks (Fig. 43). Over a thousand 
species have been preserved in this way, and we know that 
in ages past they flourished in almost incredible numbers 
and were scattered widely over the earth. Unable to adapt 
themselves to changing conditions or unable to cope with 
their enemies, they have gradually become extinct, until 
to-day scarcely more than one hundred species are known. 
These are often of local distribution, and many are com- 
paratively rare. 

For a long period the Brachiopods, owing to their pecul- 
iar shells, were classed together with the clams and other 
bivalve mollusks. The presence of a mantle also strength- 
ened the belief ; but closer examination during more recent 
years has shown that the shells are dorsal and ventral, and 
not arranged against the sides of the animal as in the 
clams. Another peculiar structure consists of two great 
spirally coiled " arms," which are comparable in a general 
way to greatly expanded lips. The cilia on these create, in 
the water currents which sweep into the mouth, the small 
animals and plants that serve as food. The internal organ- 
ization resembles in a broad way that of the animals con- 
sidered in the previous section, and it now appears that 
both trace their ancestry back to the early segmented 
worms. 

73. Band or nemertean worms. — In a few cases band or 
nemertean worms have been discovered in damp soil or in 
fresh-water streams. These are commonly small and incon- 
spicuous, and are pigmies when compared witli their marine 
relatives, which sometimes reach a length of from fifty to 
eighty feet. Many of the marine species (Fig. 44) are often 
found on the seashore under rocks that have been exposed 



ANIMALS OF UNCERTAIN RELATIONSHIPS 



71 



by the retreating tide. They are usually highly colored 
with yellow, green, violet, or various shades of red, and are 
so twisted into tangled 
masses that the differ- 
ent parts of the body 
are indistinguishable. 
As the animal crawls 
about, a long thread- 
like appendage, the pro- 
boscis, is frequently shot 
out from its sheath at 
the forward end of the 
body and appears to be 
used as a blind man 
uses his stick. At other 
times, when small worms 
and other animals are 

encountered, the proboscis is shot out farther and with 
greater force, impaling the victim on a sharp terminal spine 
(Fig. 44). The food is now borne to the mouth, located 
near the base of the proboscis, is passed into the digestive 
tract, traversing the entire length of the body, and is far- 
ther operated on by systems of organs too complex to be 
considered here. 




Fig. 44.— A band or nemertean worm. A, entire 
worm ; B, head, bearing numerous eyes and 
spine-tipped proboscis. 



CHAPTER VIII 

MOLLUSKS 

74. General characters. — For very many years the mol- 
lusks — that is, the clams, snails, cuttlefishes, and their allies 
— have been favorite objects of study largely because of the 
durability, grace, and coloration of the shell. The latter 
may be univalve, consisting of one piece, as in the snails, or 
bivalve, as in the clams and mussels, and may possess almost 
every conceivable shape, and vary in size from a grain of 
rice to those of the giant clam (Tridacna) of the East Indian 
seas, which sometimes weighs five hundred pounds. These 
external differences are but the expression of many internal 
modifications, which, while adapting these animals for dif- 
ferent modes of life, are yet not sufficient to disguise a 
more fundamental resemblance which exists throughout 
the group. In some respects the mollusks show a close 
resemblance to the annelid worms, but, on the other hand, 
the body is usually more thick-set and totally devoid of any 
signs of segmentation. In every case the skin is soft and 
slimy, demanding moist haunts and usually the protection 
of a shell, and the body is modified along one surface to 
form a foot or creeping disk which serves in locomotion. 
The internal organization is, somewhat uniform, and will 
admit of a general description later on. Mollusks are 
divided into three classes, viz. : The Lamellibranchs, em- 
bracing the clams; the Gasteropods, or snails; and the 
Cephalopods, or cuttlefishes, squids, and related forms. 

75. Lamellibranchs (clams and mussels). — Numerous rep- 
resentatives of this class, such as the clams and mussels, 

72 



MOLLUSKS 1?> 

occur along our seacoasts or are plentifully distributed in 
the fresh-water streams and lakes. They are distinguished 
from other mollusks by a greatly compressed body, which 
is enclosed in a shell consisting of two pieces or valves 
locked together by a hinge along the dorsal surface. Rais- 
ing one of these valves, the main part of the body may be 
seen to occupy almost completely the upper (dorsal) part 
of the shell (Fig. 45), and to be continued below into the 
muscular hatchet-shaped foot (ft.), which aids the clam in 
plowing its way through the sand or mud in which it lives. 
Arising on each side of the back of the animal and extend- 
ing its entire length is a great fold of skin, which com- 
pletely lines the inner surface of the corresponding valve 
of the shell. These are the two mantle lobes (m) instru- 
mental in the formation of the shell, and enclosing between 
them a space containing the foot and a number of other 
important structures, the most conspicuous of which are 
the gills (#), consisting of two broad, thin plates attached 
along the sides of the animal and hanging freely into the 
space (mantle cavity) between the mantle and the foot. 
Owing to this lamella-like character of the branchia or gills 
the class derives its name, lamellibranch. To illustrate the 
relations of these various organs to one another the clam has 
been compared to a book, in which the shells are repre- 
sented by the cover, the fly-leaves by the mantle lobes, the 
first two and last two pages by the gills, and the remaining 
leaves by the foot. In the clams, however, the halves of 
the mantle, like the halves of the shell, are curved, and 
tli us enclose a space, the mantle cavity, which is partly 
filled by the gills and foot. 

Unlike the other mollusks which usually lead active 
and more aggressive lives, the clams show scarcely a sign of 
a head and tentacles, and other sense organs are likewise 
absent from this region. The mouth also lacks definite 
organs of mastication, and as devices for catching and 
holding food are not developed, the food is brought to the 



n 



ANIMAL FORMS 



mouth by means of the cilia on the great triangular lips 
palps which bound it on each side (Fig. 45, A,p). 

It i 



or 




PlG. 15.— Anatomy of freshwater clam. A, right valve of shell removed ; B, dissec 
tion to show internal organs, a, external opening of kidney ; a.a., the anterior 
muscle for closing the shell ; b. opening of reproductive kidney ; c, brain ; ft. % 
foot ; f/. gill ; h, heart ; i. intestine; &, kidney ; /. liver; 7/1, mantle (upper fig.), 
month dower fig.); />. palp (upper flg.)i foot nerves (lower fig.); p. a., hinder 
muscle for closing the shell ; *, space through which the water passes on 
leaving the body ; %t % Btomacb ; v, nerves snpplying'viscera. 

Between the halves of the shell in the hinge region is a 
horny pad that acts like a spring, and without any muscu- 
lar effort on the part of the clam keeps the shells open. 



MOLLUSKS 75 

These are also united by two great adductor muscles, located 
at opposite ends of the animal (Fig. 45, A, a.u., p.a.)^ which 
in times of disturbance contract and firmly close the shell. 
Upon their relaxation the shell opens, the clam extends its 
foot, and plows its way leisurely through the mud, or re- 
mains buried, leaving only the hinder portion of its gaping 
shell exposed. Through this opening a current of water 
is continually passing in and out, owing to the action of 
the cilia covering the gills, and by placing a little car- 
mine or coloring matter in the ingoing stream we may 
trace its course through the body. Passing in between the 
mantle and the foot it travels on toward the head, giving 
off small side streams which are continually made to enter 
minute openings in the gills, whence they are conducted 
through tubes in each gill up to a large canal at its base, 
where it is carried backward to the exterior. In this pro- 
cess oxygen gas is supplied to the number of blood-ves- 
sels traversing the gills, and at the same time considerable 
quantities of minute organisms and organic debris are 
hurried forward toward the head, where they encounter the 
whirlpools made by the cilia on the lips and are rapidly 
whisked down into the mouth and swallowed. 

75. Rock- and wood-boring clams.— Other similar forms 
are rendered even more secure through their ability to 
bore in solid rock. In the common Piddock, for example 
(Fig. 46), the shell is beset with teeth like a rasp, which 
gradually enlarge the cavity as the animal grows, until it 
becomes a prisoner with no means of communication with 
the exterior save the small opening through which the 
siphons project. This is also the case with the Teredo, 
improperly called the shipworm, which swims about for 
some time during early life and then, about the size of a 
small pinhead, settles down upon the timbers of wharves 
or unsheathed ships, into which it rapidly tunnels. 
Throughout life its excavation is extended sometimes to a 
distance of two to three feet, and imprisoned yet safe at 



76 



ANIMAL FORMS 



the bottom of its burrow, it extends its slender siphons up 
the tube and out of the entrance for its food supply. 
Often hundreds of individuals enter the same piece of 
wood, which becomes thoroughly riddled within a short 




Pig. 16.— The piddock (Zirphcea crispata), a rock-boring 

from life. 



Natural size. 



time, and though giving no outward sign of weakness may 
collapse with its own weight. Incalculable damage is thus 
rendered to the shipping interests, and in consequence 
much has been done to check their ravages, but they are 
far from being completely overcome. 

7G. Other stationary species. — A large number of other 
species, while small and inconspicuous, arc also free to 



3I0LLUSKS 



77 



move about, but as they become larger they lose this ability 
either wholly or periodically. In the edible mussels (Myti- 
lus, Fig. 47), for example, which are associated in great 
numbers on the rocks along our coasts, the foot early be- 
comes long and slender and capable of reaching out a con- 
siderable distance from the shell to attach threads (byssus), 
which it spins, to foreign objects. These are remarkably 
strong, and when several have been spun it becomes a mat- 
ter of much difficulty to dislodge them. After remaining 
anchored in one situation for a while the mussel may vol- 




FlG, 



47.— The edible mussel {MytUus edulis), showing the threads by which it is 
attached. Natural size, from life. 



untarily free itself, and in a labored fashion move to some 
other more favorable spot where it again becomes attached, 
but there are numerous species, such as "fan shells" 
(Pinna), scallops, Anomia, and a few fresh-water forms, 
where the union is permanent. 

Finally, in the oysters, some of the scallops, and a num- 
ber of less familiar forms, the young in very early life drop 
down upon some foreign object to which the shell soon 
becomes firmly attached, and in this same spot they pass 
the remainder of their lives. The oyster usually falls upon 
the left half of its shell, which becomes deep and capacious 
enough to contain the body, while the smaller right valve 



78 ANIMAL FORMS 

acts as a lid. As locomotion is out of the question, the foot 
never develops, and the shell is held by only one adductor 
muscle, whose point of attachment in the oyster is indicated 
by a brown scar in the interior of the shell. 

77. Internal organization. — It is thus seen that the ex- 
ternal features of the clam are variously modified, according 
to the life of the animal, but the internal organization is 
much more uniform. In nearly every species the food con- 
sists of floating organisms, which are driven by the palps 
into the mouth and on to the simple stomach, where it is 
subjected to the solvent action of the fluids from the liver 
(Fig. 45, B, I) before entering the intestine. This latter 
structure is usually of considerable length, and in the active 
species extends down into the foot, and it is also peculiar in 
penetrating the ventricle of the heart. Traversing the in- 
testine the nutritive portion of the food is absorbed, and is 
conveyed over the body by a circulatory system more highly 
developed than in the higher worms. On the dorsal side 
of the clam, in a spacious pericardial chamber, the large 
heart is situated (Fig. 45, 7^), consisting of a median highly 
muscular ventricle surrounding the intestine and of two 
thin auricles, one on either side. From the former, two 
arteries with their numerous branches convey the blood to 
all parts of the body, where it accumulates, not in capilla- 
ries and veins, but in spaces or sinuses among the muscles 
and various organs, constituting a somewhat indefinite sys- 
tem of channels, which lead to the gills and kidneys. In 
these latter organs the blood delivers up the waste which it 
has accumulated on its journey, and absorbing a supply of 
oxygen, it flows into the great auricles, which in turn pass 
it into the ventricle to circulate once more throughout 
the body. 

The excretory apparatus, consisting usually of two kid- 
neys, of which one may degenerate in many snails, bears a 
close resemblance to that of the annelids. In the clam, for 
instance, each consists of a bent tube symmetrically ar- 



MOLLUSKS 79 

ranged on each side of the body (Fig. 45, B, &), and the inner 
ends (a), corresponding to the ciliated funnel of the anne- 
lid kidney, open into the pericardial cavity. Their walls 
are continually active in extracting wastes from the blood 
supplied to them, and these, together with the substances 
swept out from the pericardial cavity, traverse the tube and 
are carried to the exterior. In other mollusks the kidney 
may be more compact, or greatly elongated, or otherwise 
peculiar, but in reality they bear a close resemblance to 
those of the clam. 

78. Nervous system. — The nervous system, like the ex- 
cretory, differs considerably in different mollusks, yet the 
resemblances are fairly close throughout. In the clam the 
cerebral ganglia corresponding to the u brain " in annelids 
is located at either side, or above the mouth, and from it 
several nerves arise, the larger passing downward to two 
pedal ganglia (;;) embedded in the foot and to the visceral 
ganglia (v) far back in the body (Fig. 45, B). These nerve 
centers continually send out impulses which regulate the 
various activities of the body and also receive impressions 
from without. These come chiefly through the sense of 
touch, for in the clams the other senses are usually either 
feebly developed or altogether absent. 

79. Development. — In the mollusca new individuals al- 
ways arise from eggs, which are commonly deposited in the 
water and there undergo development. In the fresh-water 
clams the reproductive organ is usually situated in the foot 
(Fig. 45), while in the oyster and similar inactive species it is 
attached to the large adductor muscle. In these latter, and 
in many other marine forms, the eggs are shed directly into 
the sea, where they are left to undergo their development 
buffeted by winds and waves and subject to the attack of 
numerous enemies. Under such circumstances the chances 
of survival are slight, and for this reason eggs are laid in 
vast numbers, which have been variously estimated for the 
oyster, for example, from two to forty million. Develop- 



80 ANIMAL FORMS 

ment proceeds at first much as in the sponge, but soon the 
shell, foot, gills, and various other molluscan structures 
put in an appearance, and the few surviving young which 
have been free-swimming now settle down in some favor- 
able spot, and attach themselves or burrow according to 
their habit. 

80. Life history of fresh-water clams. — The life history of 
our common fresh-water clams is perhaps one of the most 
remarkable known among mollusks. The parent stores the 
eggs, as soon as they are laid, in the outer gill plate, and 
there, well protected, they undergo the first stages of their 
development, which results in the formation of minute 
young enclosed in a bivalve shell beset with teeth. These 
are often readily obtained, sometimes as they are escaping 
from the parent, and when examined under the microscope 
are seen to rapidly open and close their shells in a snapping 
fashion when in the least disturbed. In a state of nature 
this latter movement may result in attaching the young to 
the fins or gills of some passing fish, which is necessary to 
its further development. Within a short time it becomes 
completely embedded in the flesh of its' host, from which, 
as a parasite, it draws its nourishment, and during the 
next few weeks undergoes a wonderful series of transforma- 
tions resulting in a small mussel, which breaks its way 
through the thin skin of the fish and drops to the bottom. 

81. The gasteropods. — The gasteropods, including snails, 
slugs, limpets, and a host of related forms, fully twenty 
thousand different species in all, are found in most of our 
fresh-water streams and lakes and in moist situations on 
land, while great numbers live along the seashore and at 
various depths in the ocean, even down as far as three 
miles. Examining any of them carefully we find many of 
the same organs as in the clams, but curiously changed and 
adapted for a very different and usually active life. In our 
common land snails (Fig. 48), which we may well examine 
before passing on to a general survey of the group, the first 



MOLLUSKS 



81 



striking peculiarity is in the univalve shell, with numerous 
whorls, into which the animal may at any time withdraw 
completely. Ordinarily this is carried on the back of the 
spindle-shaped body, which is fashioned beneath into a great 




Fiu. 48.— The slug {Ariolimax) and common snail {Helix). From life. 

flat sole or creeping surface that bears on its forward bor- 
der a wide opening through which mucus is continually 
issuing to enable the snail to slip along more readily. Slime 
also exudes on other points on the surface of the body and 
affords a valuable protection against excessive heat and 
drought. 

Unlike the clams, the forward end of the body is devel- 
oped into a well-marked head bearing the mouth and a 
complicated mechanism for gathering and masticating food, 
together with two pairs of tentacles, one of which carries the 
eyes. On the right side of the animal, some distance behind 
the head, is the opening of the little sac-like mantle cavity 
(Fig. 48) which contains the respiratory organs, and into 
which the alimentary canal and the kidneys pour their 
wastes. The relation of these organs to the mantle cavity 
is the same as in the clams, though the cavities differ much 
in size and position. 

82. Other snails. The shell. — Extending our acquaint- 
ance to other species of snails, we find the same general 
plan of body, although somewhat obscured at times by 



82 



ANIMAL FORMS 






n^ 








-jg ; 



many modifications. A foot is generally present, also a 
more or less well-developed head, and the body is usually 
surrounded by a shell which varies widely in shape and 
size in different species. In the common limpets the early 
coiled shell is transformed into an uncoiled cap-like one, 
and in the keyhole limpets is perforated at its summit. The 

chitons or armadillo- 
snails (Fig. 49), often 
found associated with 
the limpets, carry a 
most peculiar shell con- 
sisting of eight plates, 
which enables the ani- 
mal to roll up like an 
armadillo when dis- 
turbed. A shell is by 
no means a necessity, 
however, for in many 
species, such as the 
beautiful naked snails 
or Xudibranchs (Fig. 
50) common along our coasts, it may be entirely absent, 
or, as in the ordinary slugs, reduced to a small scale em- 
bedded in the skin. 

83. Respiration. — A considerable quantity of oxygen is 
absorbed through the skin, as in all mollusks, but the chief 
part of the process is usually taken by the plume-like gills, 
one or two in number, which are located in the mantle 
cavity. In the chitons (Fig. 40) the number of gills is 
greater, amounting in some species to over a hundred, 
while in the Xudibranchs (Fig. 50) gills are absent, their 
places being taken by more or less feathery expansions of 
the skin on the dorsal surface. 

Many of the gasteropods left exposed on the rocks by a 
retreating tide retain water in the mantle cavity, from 
which they extract the oxygen until submerged again. 



Fig. 49.— The chiton, armadillo-snail or sea-cra- 
dle. The left-hand figure shows mouth in 
center of proboscis, the broad foot on each 
side of which are numerous small gills. The 
right-hand figure shows the mantle and shell, 
composed of eight plates. From life, one- 
half natural size. 



MOLLUSKS 83 

Others breathe by means of gills while under water, and by 
the surface of the body and the moist walls of the mantle 




Fig. 50.— Three different species of naked marine snails or Nudibranchs. Natural 

size, from life. 

cavity when exposed. In some of the small Littorinas 
attached so far from the sea as to be only occasionally 
washed by the surf this latter method may prevail for days 
together — in fact they live better out of water than in it. 
It is nob difficult to imagine that such forms, keeping in 
moist places, might wander far from the sea, and, losing 
their gills, become adapted to a terrestrial life. It is 
believed that in past times this has actually occurred, and 
that our land forms trace their descent from aquatic ances- 
tors. To-day they breathe by a lung — that is, they take 
oxygen through the walls of the mantle cavity, as the slug 
may be seen to do, though in some species traces of the old 
gill yet remain. 

84. Food and digestive system. — Many mollusks live upon 
seaweeds, and the greater number of terrestrial forms are 
fond of garden vegetables or certain kinds of lichens, but, 
on the other hand, the latter, together with a large number 
of marine snails, are carnivorous. In all cases the food 
requires to be masticated, and, unlike the clams, the mouth 
is usually provided with horny jaws, and an additional 



Si 



ANIMAL FORMS 



masticatory apparatus which consists of a kind of tongue 
with eight to forty thousand minute teeth in our land 
forms (Fig. 51), while in certain marine snails they are 
beyond computation. With the licking motion of the 
tongue this rasp tears the food into shreds before it is 
swallowed, and in the whelks or borers it serves to wear a 
circular hole through the shells of other mollusks, which 

are thus killed and devoured. 

This latter process is facili- 



tated by the secretion of the 
salivary glands, which has a 
softening effect upon the 
shell. Ordinarily the saliva 
o\ snails exercises some di- 
gestive action. 




Kit;. 51. —A small portion o( the radula or 
tongue rasp of a snail (SyCOtypilS). 



In the stomach of some 
snails are teeth or horny 
ridges which also are instrumental in crushing the food, 
and in numerous minor respects peculiarities exist in differ- 
ed species according to the nature of the food; but in its 
general features the digestive tract is similar to that of 
the clams. 

The processes of circulation and excretion are also car- 
ried on by means of systems which show a certain resem- 
blance to those o\' the clams. As might be expected, certain 
differences exist, sometimes very great, but they are of too 
technical a nature to concern us further, 

85. Sense-organs of lamellibranchs and gasteropods. — 
The eyes of mollusks differ widely in their structure and 
the position they occupy in the body. In our common 
land snails two pairs of tentacles are borne on the head, 
the lower acting as feelers, while each of the upper ones 
bears on its extremity the eye, appearing as a minute black 
dot (Fig. IS). In this same position the eyes of many 
marine snails occur, but there are numerous species in 
which there are other accessory eyes. In many of the 



MOLLUSKS 85 

limpets, for instance, there are numbers of addition;il eves 
carried on the mantle edge just under the eaves of the 
shell, and forming a row completely encircling the body. 
(In the scallops there are two rows of brilliantly colored 
eyes, set like jewels on the edges of the mantle just within 
the halves of the shell.) In the chitons the eyes of the 
head disappear by the time the animal attains maturity, 
and in some species at least their place appears to be taken 
by great numbers of eyes, sometimes thousands, which are 
embedded in the shells. On the other hand, eyes are com- 
pletely absent in certain species of burrowing snails and in 
several living in the gloomy depths of the sea far from the 
surface ; they appear to be absent also from fresh-water 
clams; but the fact that certain species close their shell 
when a shadow falls upon them, leads to the belief that 
while actual eyes are not present the skin is extremely 
sensitive to light. This is also the case with many snails. 

86. Smell. — Since the sense of sight is generally unde- 
veloped in the mollusks, they rely chiefly upon touch and 
smell for recognizing the presence of enemies and food. 
Tentacles upon the head and other parts of the body, and 
a skin abundantly supplied with nerves, show them to pos- 
sess a high degree of sensibility ; but in the greater num- 
ber of species the sense of smell is of chief importance. 
Many experiments show that tainted meat and strongly 
scented vegetables concealed from sight and several feet 
distant from many of our land and sea mollusks will attract 
them at once. In these forms the sense of smell appears to 
be located on the tentacles, but additional organs, possibly 
of smell, are located on various portions of the body, usu- 
ally in the neighborhood of the gills. 

87. Taste and hearing. — Several mollusks appear to be 
almost omnivorous, but others are decidedly particular in 
their choice of food, which leads us to suspect that they 
possess to some extent the sense of taste. Nerves supply- 
ing the base of the mouth have also been detected, which 



86 ANIMAL FORMS 

may be those of taste ; but experiments along the line are 
difficult to perform, and our knowledge of this subject is 
far from complete. The same is true of hearing. Certain 
organs, interpreted as ears and located in the foot, have 
the form of two hollow sacs, containing one or more solid 
particles of sand or lime, whose jarrings, when effected by 
sonorous bodies, may result in hearing. On the other hand, 
it is held by some that they, like the semicircular canals of 
higher animals, may regulate the muscular movements 
which enable the animal to keep its balance. 

88. Egg-laying habits and development. — The egg-laying 
habits of the gasteropods differ almost as widely as their 
haunts. The terrestrial forms lay comparatively few eggs, 
ranging in size from small shot to a pigeon's egg in some 
of the tropical species. These are buried in hollows in the 
ground or under sticks and stones, and after a few weeks 
hatch out young snails having the form of the adult. The 
same is also true of most of the fresh-water snails, which 
lay relatively smaller eggs embedded in a gelatinous mass 
frequently found attached to sticks and leaves, or on the 
walls of aquaria in which they are confined. Many marine 
species construct capsules of the most varied patterns 
which they attach to different objects, and in these the 
young are protected until they hatch. In the limpets and 
many of the chitons the eggs are laid by thousands directly 
in the water, and after a short time develop into free-swim- 
ming young, differing considerably from the parent in ap- 
pearance. Those escaping the ravages of numerous enemies 
finally settle down in a favorable situation and gradually 
assume the form of the adult. 

89. Age, enemies, and means of defense of lamellibranchs 
and gasteropods. — How much time is consumed by the young 
in growing up, and the length of time they live, are ques- 
t ions generally unsettled. It is said that the oyster requires 
five years to attain maturity, and lives ten years ; the fresh- 
water clam develops in five years, and some species live from 



MOLLUSKS 87 

twelve to thirty years ; and the average length of life of 
the snail appears to be from two to five years. Certain it 
is that mollusks have numerous enemies besides man which 
prevent multitudes from living lives of normal length. 
Birds, fishes, frogs, and starfishes beset them continually, 
and many fall a prey to the ravages of internal parasites or 
to other mollusks. Under ordinary circumstances the shell 
is sufficient protection, and the spines disposed on the sur- 
face in many species render the occupant still less liable to 
attack. Many snails carry on the foot a horny or calcare- 
ous plate known as the operculum, which closes the en- 
trance of the shell like a door against intruders. Certain 
noxious secretions poured out from the skin also serve as a 
means of defense, and many Xudibranchs (Fig. 50) bear 
nettle-cells on the processes of the body, which probably 
render them distasteful to many animals. Finally, there 
are numerous clams, mussels, snails, and slugs whose colors 
harmonize so closely with their surroundings that they al- 
most completely baffle detection, and enable them to lead 
as successful a life as those provided with special organs of 
defense. 

90. Cephalopods. — The animals belonging to this class, 
such as the squids and cuttlefishes (Fig. 52), are by far 
the most highly developed mollusks. They are of great 
strength, capable of very rapid movements, and several spe- 
cies are many times the largest invertebrates. In almost 
every case there is a well-defined head bearing remarkably 
perfect eyes, and also a circle of powerful arms provided 
with numerous suckers which aid in the capture of food 
(Fig. 52). Posteriorly the body is developed into a pointed 
or rounded visceral mass which to a certain extent is free 
from the head, giving rise to a well-marked neck. Some 
forms, such as the squids (Fig. 52, upper figure), are pro- 
vided with fins which drive the animal forward, but in com- 
mon with other cephalopods they are capable of a very rapid 
backward motion. By muscular movements water is taken 
7 



88 



ANIMAL FORMS 



into the large mantle cavity within the body, a set of valves 
prevents its exit through the same channels, and upon a 
vigorous contraction of the body walls the water is forced 
out rapidly through the small opening of the funnel, which 




Fig. 52.— Cephalopoda. Lower figure, the devil-fish or octopus {Octopus punctatus). 
The upper figure represents the squid (Loligo pealii) swimming backward by 
driving a stream of water through the small tube slightly beneath the eyes. From 
life, one-third natural size. 

drives the animal backward after the fashion of an explod- 
ing sky-rocket. In this way they usually escape the fishes 
and whales that prey upon them, but an additional device 
lias been provided in the form of a sac within the body, 
whose inky contents may be liberated in such quantity as 
to cloud the water for a considerable distance, and thus 
enable them to slip away unseen into some place of safety. 
.Most of the cephalopods are further protected by their 
ability to assume, like the chameleon, the color of the object 



MOLLUSKS 89 

upon which they rest. In the skin are embedded multi- 
tudes of small spherical sacs filled with pigments of various 
colors, chieily shades of red, brown, and blue, each sac be- 
ing connected with a nerve and a series of delicate muscles. 
If the animal settles upon a red surface, for example, a 
nerve impulse is sent to each of the hundreds of color sacs 
of corresponding shade, causing the muscles to contract 
and flatten the bag like a coin, and thus exposing a far 
greater surface than before, they give the animal a reddish 
hue. In the twinkling of an eye they may completely 
change to another tint, or present a mottled look, and some 
may even throw the surface of the skin into numerous 
small projections that make the animal appear part of the 
rock upon which it rests. These devices not only serve for 
protection, but they also aid in enabling these mollusks to 
steal upon their prey, chiefly fishes, which they destroy in 
great numbers with lionlike ferocity. 

The devil-fishes and a number of other species are usu- 
ally found creeping along the sea bottom, generally near 
shore, and are solitary in their habits, while the squids re- 
main near the surface and frequently travel in great com- 
panies, sometimes numbering hundreds of thousands. In 
size they usually range from a few inches to a foot or two 
in length, but a few devil-fishes and squids attain a greater 
size, some of the latter reaching the enormous length of 
from forty to sixty feet. There are many stories of their 
great strength and of their voluntarily attacking people 
and even overturning boats, but the latter are in almost 
every case sailors' yarns. 

In their external organization the cephalopods have 
little to remind one of any of the preceding mollusks, and 
their internal structure shows only a distant resemblance. 
In the Octopi (Fig. 52) the shell is lacking ; in the squid it 
is called the pen, and consists of a horn-like substance with- 
out any lime deposit ; in the cuttlefishes it is spongy and 
plate-like, and is a familiar object in the shops ; and, finally, 



90 ANIMAL FORMS 

in the nautilus it is coiled and of considerable size, and, un- 
like that of any other cephalopod, it is carried on the out- 
side of the animal. Interiorly it is divided by a number of 
partitions into chambers, the last one of which is occupied 
by the animal. 

The alimentary canal shows some resemblance to that 
of other mollusks, but, as in the case of the other systems 
of the body, it possesses a far higher state of development. 
The mouth is situated in the center of a circle of arms, 
which in reality are modified portions of the foot, and is 
furnished with two parrot-like jaws. From this point the 
esophagus leads back into the body mass to the stomach, 
which with the liver and intestine are sufficiently like 
those of the clam and snail to require no further comment. 

Eespiration is effected by the skin to a certain extent, 
but chiefly by two gills (four in the nautilus), and the cir- 
culatory system, which conveys the blood to and from these 
organs and over the body with its complex heart, arteries, 
capillaries, and veins, is more highly developed than in 
any other invertebrate. 

As might be expected in animals with so great sagacity 
and cunning, the nervous system of the sense-organs reach 
a degree of development but little short of what we find in 
some of the vertebrates. The chief part of the nervous 
system is located in the head, protected by a cartilaginous 
skull, a very rare structure among invertebrates ; and while 
the different ganglia may be recognized in a general way 
and be found to correspond to a certain extent to those 
of foregoing mollusks, they are so largely developed and 
massed together that it is impossible at present to under- 
stand them fully. From this point nerves pass to all 
regions of the body, to the powerful muscles, the viscera, 
and the organs of special sense, controlling the complex 
mechanism in all its workings. 

There is no doubt that the cephalopods see distinctly 
for considerable distances, and a careful examination of 



MOLLUSKS 91 

the eye of the squids and cuttlefishes has shown them 
to be remarkably complex and in many respects to be 
constructed upon much the same plan as those of the 
vertebrates. As to the other senses not so much is known, 
but undoubtedly many species of cephalopods are possessed 
of a shrewdness and cunning not shared by any other 
invertebrates, save some of the insects and spiders, and are 
vastly more highly organized than their molluscan rela- 
tives. 

91. How species originate. — We have now examined a 
considerable portion of the animal kingdom, tracing its 
members from their simplest beginnings as single cells, 
through the formation of colonial types, and up through 
the sponges, coelenterates, worms, and mollusks. It is im- 
portant once more to note that they all perform the func- 
tions concerned in nutrition and reproduction, and only 
these. The differences which exist are those of structure. 
The Hydra and the clam, for example, perform the same 
duties, but their bodily apparatus differs widely, and the 
completeness and perfection of the work varies accord- 
ingly. The more the work to be performed by an organ- 
ism is divided up among especially adapted organs, so that 
each of the latter has, as far as possible, only one thing to 
do, the higher is the organism. 

As stated earlier in the account, it is believed that the 
more complex animals arose from the simpler ; that if we 
could trace the history of any of the great groups back 
toward their first beginnings, we would find them all to 
have originated from one ancestral form, that in turn owes 
its descent from yet simpler forms. 

Let us see something of how this has come about. We 
all know that vast numbers of young are born into this 
world which never come to maturity. It is said that if all 
the young of the codfish were to live their allotted time, 
it would be less than fifteen years before the sea would 
become literally packed with them. Numerous enemies, 



92 ANIMAL FORMS 

the lack of food, and other agencies annihilate the larger 
part. We also know that no two offspring are exactly- 
alike. They exhibit individual differences. One bird may- 
have a larger bill than another of the same brood which 
excels in length of wing. As noted above, all the offspring 
will not attain maturity. Those best adapted to their sur- 
roundings will have the best chances of survival. The 
increased length of bill or wing may be slight, but it may 
be just this amount which enables the bird to probe deeper 
or fly farther and thus secure the requisite amount of food. 
A premium is placed on length of wing or bill generation 
after generation, with the result that a long-billed species 
arises distinct from the long-winged which trace their 
ancestry back to the same parents. It is the same prin- 
ciple which enables the breeder to increase the swiftness 
of the race-horse and the strength of the draft-horse, or 
the gardener to develop from the wild rose the great num- 
ber of widely different varieties. In the same way other 
slight peculiarities over very many generations may en- 
able other forms to gradually adapt themselves to still dif- 
ferent modes of life. Thus vast numbers of organisms 
gradually become modified in form and complexity, and 
are adapted to lives which insure them a comparative 
degree of safety and less competition with other species. 



CHAPTER IX 

ARTHROPODS. CLASS CRUSTACEA 

92. General characters. — In the Arthropods, that is, the 
crabs, lobsters, shrimps, insects, spiders, and a vast host 
of related forms, the body is bilaterally symmetrical, and 
is composed of a number of segments arranged in a series, 
as in the earthworm and other annelids. A hornlike cu- 
ticle, sometimes called the shell, bounds the external sur- 
face — in early life thin and delicate, but later relatively 
thick, and often further strengthened by lime salts. Along 
the line between the segments this coat of mail remains 
thin and forms a flexible joint. Appendages also are borne 
on each segment, not comparatively short and fleshy out- 
growths like the lateral appendages of many of the worms, 
but usually long and jointed (hence the name Arthropod, 
meaning jointed foot), and variously modified for many 
different uses. 

93. Classification. — The species belonging to this group 
outnumber the remainder of the animal kingdom. Their 
haunts also are most diverse. Some are adapted for lives 
in the sea and fresh water, others for widely different sit- 
uations on land, and a great number are constructed for a 
life on the wing. A certain resemblance exists among them 
all, but the modifications which fit them for their different 
habitats are also profound, and have resulted in the division 
of the Arthropods into five classes. The first class (Crus- 
tacea) contains the crayfish, crabs, etc. ; the second (Ony- 
choplioru) includes the curious worm-like peripatus (Fig. 

9^ 



94: ANIMAL FORMS 

66) ; the third (Myriapoda, meaning myriad-footed) em- 
braces the centipeds and "thousand-legs" ; the fourth (In- 
secta) contains the insects; and the fifth (Arachnida) in- 
cludes the scorpions, spiders, and mites. 

94. The Crustacea. — The number of species of crusta- 
ceans is estimated to be about ten thousand, and while the 
greater number of these are marine, many are found in 
fresh water and a few occur on land. In size they range 
from almost microscopic forms to the giant crabs and 
lobsters. They differ also in shape to a remarkable degree, 
but at the same time there is a decided resemblance through- 
out the group, except in those species which have become 
modified by a parasitic habit. The characteristic external 
skeleton is invariably present, and gives evidence of the 
deep internal segmentation of the body. In the simple 
Crustacea this is very apparent, but in the higher forms it 
is usually more or less obscured, owing to the fusion of some 
of the different segments, especially those of the head, as in 
the crayfish (Fig. 59). 

The class of the Crustacea is subdivided into two sub- 
classes (Entomostraca and Malacostraca), the first containing 
the fairy-shrimps (Branchipus, Fig. 53) and their allies, the 
copepods (such as Fig. 54), the barnacles (Fig. 55), and a 
number of other species. In their organization all are com- 
paratively simple, usually small, and the appendages show 
relatively little specialization. The other subclass contains 
the more highly developed and usually large-sized Crustacea, 
among which are the shrimps, crayfishes, lobsters, crabs, 
and a number of other forms. 

95. Some simple Crustacea. — While the members of the 
first subclass are minute and inconspicuous, several species 
are often remarkably abundant in our small fresh-water 
pools. Among these is the beautifully colored fairy-shrimp 
(Branchipus, Fig. 53), with greatly elongated body and 
leaf-like appendages, whose relai ively simple character leads 
the zoologist to think that they are among the simplest 



ARTHROPODS. CLASS CRUSTACEA 



95 



Crustacea, and in several points resemble the ancestral form 
from which all the modern species have descended. Some 
nearly related forms are provided with a great fold of the 
body- wall, which may almost completely conceal the animal 
from above, or it may be formed like a bivalve clam-shell, 
within which the entire body may be withdrawn. This 

h 




Fig. 53.— Fairy-shrimp (Branchipns). b, brood-pouch ; e, e', 
compound and simple eyes ; /, paddle-shaped feet ; h, tu- 
bular heart ; i, intestine. 



latter character is also found in the water-fleas (Daphnia), 
very much smaller forms, and sometimes occurring in mil- 
lions on the bottoms of our ponds and marshes. They are 
readily distinguished from the fairy-shrimp by the short- 
ness of the body, the small number of appendages, and by 
their habit of using their antennae as swimming organs, 
which gives to their locomotion a jerky, awkward character. 
96. Cyclops and relatives. — Cijclops (Fig. 54), the repre- 
sentative of a number of lowly forms belonging to the order 
of Copepods, is one of the commonest fresh-water Crustacea. 
The forw r ard segments of the spindle-shaped body are cov- 
ered by a large shield or carapace, the feet are few in num- 
ber, and, like its fabled namesake, it bears an eve in the 
center of the forehead. Xearly related species are also re- 
markably abundant at the surface of the sea, at times occur- 



96 



ANIMAL FORMS 



*^fe 



1b. 



ring in such vast numbers that they impart a reddish tinge 
to the water over wide areas, and at night are largely re- 
sponsible for its phos- 
phorescence. Many oth- 
ers are parasitic in their 
habits, and scarcely a 
salt-water fish exists but 
that at one time or an- 
other suffers from their 
attacks. On the other 
hand, many fresh- and 
salt-water fishes depend 
upon the free-swimming 
forms for food, and 
hence, from an economic 
point of view, they are 
highly important organ- 
isms. 

97. Barnacles. — The 
parasitic habit and the 
lack of locomotion has 
also produced marvelous 
changes among the bar- 
nacles, so great that 
originally they were 
placed among the mol- 
lusks; and as with the parasitic copepods, their true posi- 
tion was only known after their life-history had been de- 
termined. In the goose-barnacles * the body, attached by 
a fleshy stalk to foreign objects, is enclosed by a tough 
membrane, corresponding to the carapace of other Crus- 
tacea, in which are embedded five calcareous plates. This 

* So called because of the belief, winch existed for three hundred 
years prior to the present century, Unit when mature these animals 
give birth to geese. 




Fig. 54. 



-Cyclops, e. s., eggs ; i, intestine ; 
reproductive organ. 



ARTHROPODS. CLASS CRUSTACEA 



97 



is open along one side, and allows the feather-like feet to 
project and produce currents in the surrounding water 
which brings food within reach. In the acorn-barnacles 
(Fig. 55) the stalk is absent, and the body, though possess- 




Fig. 55. — Barnacles, 



Acorn-barnacles chiefly in lower part of figure ; goose-barnacles 
above. Natural size. 



ing the same general character as the goose-barnacles, is 
shorter, and enclosed in a strong palisade consisting of six 
calcareous plates. 

The larger number of barnacles attach themselves to 
the supports of wharves, the hulls of ships, floating tim- 
bers, the rocks from the shore-line down to considerable 
depth, and a few species occur on the skin of sharks and 
whales. On the other hand, there are several species which 
arc parasitic, and in accordance with this mode of life ex- 
hibit various degrees of degeneration. In the most extreme 



98 ANIMAL FORMS 

cases (Sacculina) the sac-like body, attached to the abdo- 
men of crabs, is entirely devoid of appendages and any 
signs of segmentation. A root-like system of delicate fila- 
ments extends from the exposed part of the animal into 
the host and absorbs the necessary nutriment. The mouth 
and alimentary canal are accordingly absent — in fact, the 
body contains little but the reproductive organs and a very 
simple nervous system. 

98. Structure. — In the internal organization of these 
smaller crustaceans many differences may be noted, though 
they are usually less profound than the external. Ordi- 
narily the alimentary canal is a straight tube passing 
through the body, and is provided with a pouch-like 
stomach, and a more or less clearly defined liver. In 
all, except the parasitic species, the external mouth-ap- 
pendages masticate the food, and in a very few of the 
above-described groups it may be further ground between 
the horny ridges on the stomach-walls. After this pre- 
liminary treatment it is subjected to the action of the 
digestive juices, and when liquefied is absorbed into the 
body. Here it is circulated by a blood-system of widely 
different character. In many cases definite arteries and 
veins are absent. The blood courses through the body in 
the spaces between the different organs propelled by the 
beating of the heart, which it is made to traverse. In 
Cyclops (Fig. 54) even the heart is absent, and the blood 
is made to circulate by contractions of the intestine. In 
most of these smaller Crustacea considerable oxygen is ab- 
sorbed through the body-wall ; but in several species, for 
example, the fairy-shrimp (Fig. 53), special gills are devel- 
oped on the appendages of the body. 

99. Multiplication. — Among the Crustacea thus far con- 
sidered the males are usually readily recognized owing to 
their small size. The females also are usually provided 
with brood-pouches in which the developing eggs are pro- 
tected. In almost every case the young are born in the 



ARTHROPODS. CLASS CRUSTACEA 



99 



form of minute larvae, provided with three pairs of append- 
ages, a median eye (Fig. 5G), and a firm external skeleton 
or cuticle. This latter prevents the continuous growth of 
the larvae or nauplhis, and every few days it is thrown oft', 
and while the new one is forming the body enlarges. Dur- 
ing this time new appendages are developed, so that after 
each moult the young crusta- 
cean emerges less like its 
former self and more and more 
like its parents. In the bar- 
nacles, after several moults 
have taken place, the young 
become permanently attached 
by means of their first anten- 
nae, their thoracic feet change 
into feathery appendages, and 
several other changes occur. 
In some of the parasitic bar- 
nacles (Sacculina) the larva 
attaches itself to a crab, throws 
off its various appendages, and, 
after other great degenerative 
changes, enters its host. For 
a time, therefore, their development is toward greater com- 
plexity, but the later stages constitute a retrograde meta- 
morphosis. 

100. More complex types. — The larger, more useful, and 
usually more familiar Crustacea belong to the second divi- 
sion (subclass Malacostraca). It comprises such animals as 
the shrimps, crayfish, lobsters, crabs, and a number of other 
forms which are at once distinguished from the preceding 
by the constant number of segments composing the body. 
Of these, five constitute the head, eight the thorax, and 
seven the abdomen. The head segments are always fused 
ther, and with them one or more thoracic segments 
unite to form a more or less complete cephalothorax. Also, 
LofC. 




Fig. 56. — Development of a barnacle 
(Lepas). «, larva ; b, adult. 



100 



ANIMAL FORMS 



some of the head segments give rise to a great fold of the 
body-wall, the carapace, which extends backward and covers 
all or a part of the thorax, with which it may firmly unite, 
as in the crayfish. The appendages are usually highly spe- 
cialized, and are made to perform a variety of functions. 

101. The shrimps. — Among the simplest of these are the 
opossum-shrimps (Fig. 57) and their relatives, small trans- 




Fig. 57.— The opossum-shrimp (Mysis americana). 

parent creatures often seen swimming in great numbers at 
the surface of the sea or hiding among the seaweeds along 
the shore. In general appearance they resemble crayfishes 
or prawns, but are readily distinguished by the two-branched 
thoracic feet. This " split-foot " character also occurs 
among many of the preceding Crustacea, and is generally 
a badge of low organization, tending to disappear in the 
more highly organized forms. In this and other respects 
the shrimps are especially interesting in their relation to 
the preceding Crustacea, and in the fact that they may 
closely resemble the ancestors of the modern prawns (Fig. 
58), lobsters, crayfishes, and crabs. 

102. Crayfishes and lobsters. — The last-mentioned spe- 
cies and their allies, usually large and familiar forms, con- 
stitute a group known as the decapods (meaning ten feet), 
referring to the number of thoracic feet. Among the mem- 
bers of this division probably none are more familiar than 
the crayfishes, which occur in most of the larger rivers and 
their tributaries throughout the United States and Europe. 
It is their habit to remain concealed in crevices of rocks 



ARTHROPODS. CLASS CRUSTACEA 



101 



or in the mouths of the burrows which they excavate, and 
from which they rush upon the small fish, the larvae of 




Fig. 58.— Prawn (Heptacarpm brevirostris). 

many animals, and other equally defenseless creatures 
which constitute their bill of fare. In turn they are 
eagerly sought by certain birds and four-footed animals, and, 
especially in France, 
are extensively used for 
food by man. 

Closely related to 
the crayfishes and dif- 
fering but little from 
them structurally are 
the lobsters. In this 
country they are con- 
fined to the rocky coasts 
from Xew Jersey to 
Labrador, living upon 
fish, fresh or otherwise, 
various invertebrates, 
and occasionally sea- 
weeds. Far more than 
the crayfish, the lobster 
is in demand as an arti- 
cle of food. By the aid 
of nets or various traps 




Fiu. 59.— The crayfish (Astacus). 



102 ANIMAL FORMS 

millions are caught each year, and to such an extent has 
their destruction proceeded that in many places they are 
well-nigh exterminated. At the present time, however, leg- 
islation, numerous hatcheries, and a careful study of their 
life habits is doing much to better matters and inciden- 
tally to put us in possession of many interesting zoological 
facts along this line, some of which will be mentioned later. 
Frequently the prawns, especially the larger ones, and a 
spiny lobster (Palinurus), are mistaken for crayfishes or 
lobsters, but they differ from them in the absence of the 
large grasping claws. 

Along almost any coast some of these animals are to be 
found, often beautifully colored and harmonizing with the 
seaweeds among which they live, or so transparent that 
their internal organization may be distinctly seen. Farther 
out at sea other species swim in incredible numbers, feed- 
ing upon minute organisms, and in turn fed upon by numer- 
ous fishes and whales ; and, especially on the Pacific coast, 
shrimp-fishing is an important industry. 

103. The hermit-crabs. — The last of these long-tailed 
decapods is the interesting group of the hermit-crabs, 
which occur in various situations in the sea. In early life 
they take possession of the empty shell of some snail, and 
the protected abdomen becomes soft and flabby, while the 
appendages in this region almost completely disappear. 
The front part of the body, on the other hand, continually 
grows in firmness and strength, and is admirably adapted 
for the continual warfare which these forms wage among 
themselves. As growth proceeds the necessity arises for a 
larger shell, and the crab goes "house-hunting" among the 
empty shells along the shore, or it may forcibly extract the 
snail or other hermit from the home which strikes its fancy. 

Many of the hermit-crabs enjoy immunity from the 
attacks of their belligerent relatives by allowing various 
hydroids to grow upon their homes. Others attach sea- 
anemones to their shells or to one of their large claws, 






ARTHROPODS. CLASS CRUSTACEA 



103 



which they poke into the face of any intruder. While 
the anemones or hydroids are made to do valiant service 




Fig. 60.— Hermit-crab {Pagurus bernhardus) in snail shell covered with Hydractinia. 

with their nettle-cells, they also enjoy the advantages of 
a large food-supply which is attendant upon the free ride. 

104. The crabs. — The most highly developed Crustacea 
are the crabs or short-tailed decapods which abound between 
tide-marks alongshore, and in diminishing numbers extend 
to great depths. The cephalothorax is usually relatively 
wide, often wider than long, and the greatly reduced abdo- 
men is folded against the under side of the thorax. Corre- 
lated with the small size of the abdomen, the appendages 
of that region disappear more or less, but the remaining 
appendages are similar to those of the crayfish or lobsters. 
All these different parts, however, are variously modified in 
each species to fit it for its own peculiar mode of life. In 
some forms, such as the common cancer-crab (Fig. 61), the 
legs are comparatively thick-set and possessed of great 
strength, enabling them to defend themselves against most 
enemies. On the other hand, there are the spider-crabs 
with small bodies and relatively long legs, withal weak, and 
8 



104 



ANIMAL FORMS 



yet so harmonizing with their surroundings that they are 
as likely to survive as their stronger relatives. In this 




Fig. 01.— Kelp-crab {Epialtus productus) in upper part of figure ; to the right the 
edible crab ( Cancer productus), and the shore-crab {Pugettia richii). 

connection it is interesting to note that the giant crab of 
Japan, the largest crustacean, being upward of twenty feet 
from tip to tip of the legs, is a spider-crab, constructed on 




Fig, 62.— The fiddler-crab I Oelasimw). Photograph by >lis> Mahv Rathbun. 

the saiiH 1 general pattern as our common coast forms. 
Between these two extremes numberless variations exist, 



ARTHROPODS. CLASS CRUSTACEA 



105 



some for known reasons, but more often not readily under- 
stood. And not only does the form vary, but the external 
surface may be sculptured or beset with spines or tubercles 
which frequently render the animal inconspicuous amid its 
natural surroundings. Such an effect is heightened by the 
presence of sponges, hydroids, and various seaweeds which 
the crab often permits to gather upon its body. 

105. Pill-bugs and sandhoppers. — Finally there remain the 
groups of the pill- or sow-bugs (Isopods) and the sand-fleas 
or sandhoppers (Amphipods). In the first of these the 
body is usually small and compressed, the thorax more or 
less plainly segmented, and the seven walking (thoracic) 
legs are similar. In the female each leg bears at its base a 
thin membranous plate which extends inward and hori- 



• 



M 



m 



% 



w%~ii&s 



9r- v 





Fig. 63.— Isopod or pill-bug (Porcellio laevis). 

zontally, thus forming on the under side of the body a 
brood-pouch (Fig. 63) in which the young develop. As 
one may readily discover in any of the common species, 
the abdominal segments are more or less fused, and bear 
appendages adapted for respiration and, in the aquatic 
forms, for swimming. 



106 



ANIMAL FORMS 



The marine isopods occur in the sand, under rocks, and 
in the seaweeds ; many are parasitic upon fishes ; and the ter- 
restrial forms (Fig. 63) are very common objects under old 




Fig. G4.— Amphipods or sand-fleas {Gammarus, upper species, and Caprella). 

logs and in cellars, where they live chiefly on vegetable mat- 
ter. In the sand-fleas the body is compressed from side to 
side, and while the thorax shows distinct segments, the legs 
are frequently dissimilar, and some may bear pincers. One 
of their most distinctive marks concerns the last three ab- 
dominal appendages, which are usually modified for leaping. 
The sand-fleas (Fig. 64) are familiar objects to any one 
who has collected along the beach and has turned over the 
cast-up seaweeds, while numbers of small species often oc- 
cur among the plants in our fresh-water ponds. Some most, 
curious and highly modified forms, whose general appear- 
ance is shown in the lower part of Fig. 64, occur among 



ARTHROPODS. CLASS CRUSTACEA 107 

hydroid colonies, with which their bodies harmonize in 
form and color. And, lastly, most bizarre creatures, known 
as " whale-lice/' attach themselves to the skin of whales, cf 
which each species acts as host for one or more kinds. 

106. Internal organization. — Most Crustacea are carnivo- 
rous, preying upon almost any of the smaller animals within 
convenient reach ; a much smaller number live on vege- 
table food ; and there are many, such as the crayfishes, lob- 
sters, and numerous crabs, which are also notorious scaven- 
gers. In these latter forms the food is held in one of the 
large pincers, torn into shreds by the other, and transferred 
to the mouth-parts, where, as in all Crustacea, it is soon 
reduced to a pulp by their rapid movements. In many 
species the food is now ready for the digestive process, 
but not so in the higher forms. If the stomach of any of 
these, for example, the crabs or crayfishes, be opened, three 
(Fig. 65, s) large teeth operated by powerful muscles will 
be noted, and beyond these a strainer consisting of many 
closely set hairs. In operation this "gastric mill "takes 
the food passed on from the mouth-parts, and crushes and 
tears it until fine enough to pass through the strainer, 
whereupon it is dissolved by the juices from the liver and 
is absorbed as it passes down the intestine. 

The circulatory system is usually highly developed, and 
consists of a heart, in some species almost as long as the 
body, though usually shorter (Fig. 65), from which two or 
more arteries branch to all parts of the body. Here the 
blood, instead of emptying into definite veins, pours into a 
series of spaces or sinuses in among the muscles and other 
organs of the body, through which it makes its way back to 
the heart. During this return journey it is usually made 
to traverse definite respiratory organs, either situated upon 
the legs or, as feathery outgrowths, upon the sides of the 
body, and generally concealed under the carapace. A por- 
tion of the blood is also continually sent to the kidneys, 
which are located either at the base of the second antennae 



108 ANIMAL FORMS 

(and known as green glands), as in the crayfishes or crabs, 
or on the second maxillae (shell-glands) in many of the 




Fig. 65.— Dissection of crayfish, b, brain ; h, heart ; i, intestine ; k, kidney ; I, liver ; 
n, nerve-cord ; r, reproductive organ ; s, stomach, showing two teeth in position. 

simpler crustaceans. Their method of operation is much 
like that of the kidneys in the earthworm. 

107. Nervous system and special senses. — The nervous sys- 
tem also shows a decided resemblance to that of the anne- 
lids. The cerebral ganglia or brain is situated above the 
alimentary canal in the head, and connects with the ven- 
trally lying cord by a collar. As in the earthworm, this 
ventral cord is double, and bears a pair of swellings or gan- 
glia in each segment. In the crayfish, crabs, and other 
highly modified forms, where the segments tend to fuse, 
several of these ganglia may also unite, and except in early 
life their number cannot be determined. 

Among the less specialized Crustacea the order of intel- 
ligence is low, though perhaps it may prove to be higher 
than is usually supposed when such forms have been more 
thoroughly studied. The following quotation relating to 
the lobster applies even more to the higher forms, the 
crabs : " Sluggish as it often appears when out of water and 
when partially exhausted, it is quite a different animal when 
free to move at will in its natural environment on the sea- 



ARTHROPODS. CLASS CRUSTACEA 109 

bottom. It is very cautious and cunning, capturing its 
prey by stealth, and with weapons which it knows how to 
conceal. Lying hidden in a bunch of seaweed, in a crevice 
among the rocks, or in its burrow in the mud, it waits until 
its victim is within reach of its claws, before striking the 
fatal blow. The senses of sight and hearing are probably 
far from acute, but it possesses a keen sense of touch and 
of smell, and probably also a sense of taste. " 

Although enclosed in a horny and often very thick and 
strong armor, the sense of touch is very keen in the 
Crustacea and in arthropods generally. On many of the 
more exposed portions delicate hairs or pits connected 
with the nervous system occur in great abundance. Some 
of these, usually on the antennae, undoubtedly serve in 
detecting odors, but the remainder are considered to be 
tactile. In the higher Crustacea, such as the crayfish, 
lobsters, and crabs, ears are usually found, consisting of 
sacs lined with similar delicate hairs, and containing sev- 
eral minute grains of sand, which in many cases make their 
way through the small external opening. Vibrations com- 
ing through the water gently shake the grains of sand, 
causing them to strike against the hairs which communi- 
cate with the nervous -system — a very simple ear, yet suffi- 
cient for the needs of the animals. 

The eyes of the Crustacea and arthropods in general are 
either simple or compound. The simple and frequently 
single eyes usually consist of a relatively few cells embedded 
in a quantity of pigment and connected with the nervous 
system. It is doubtful whether they perceive objects as 
anything more than highly blurred images, and perhaps 
they merely recognize the difference between light and 
darkness. The compound eyes, on the other hand, are 
remarkably complex structures, often borne on the tops of 
movable stalks, as in the common crabs and crayfishes. 
Each consists of an external transparent cornea, divided 
into numerous minute hexagonal areas corresponding to as 



110 ANIMAL FORMS 

many internal rods of cells, provided with an abundant 
nerve-supply. These latter elements may perhaps repre- 
sent simple eyes grouped together to form the compound 
one ; and it appears possible that each element may form 
a complete image of an object, as each of our eyes is known 
to do. On the other hand, many hold that the complete 
eye forms only one image, a mosaic, each element con- 
tributing its share. 

108. Growth and development. — As we have seen, the 
simpler Crustacea hatch as minute larvae (Fig. 56), and dur- 
ing their growth to the adult condition are especially sub- 
ject to the attacks of multitudes of hungry enemies. In 
the higher forms, such as the crabs, some of these early 
transformations take place while the young are still within 
the egg and attached to the parent. Accordingly, the little 
ones are fairly similar to their parents, and their later his- 
tory is very well exemplified by the lobster. 

The eggs of the lobster are most frequently hatched in 
the summer months, usually July, after they have been 
carried by the parent for upward of a year. The young, 
about a third of an inch in length, at once disperse, undergo 
four or five moults during the next month, then, ceasing 
their swimming habits, settle to the bottom among the 
rocks. At this time, twice their original size, they closely 
resemble their parents, and their further development is 
largely an increase in size. " The growth of the lobster, 
and of every arthropod, apparently takes place, from in- 
fancy to old age, by a series of stages characterized by the 
growth of a new shell under the old, by the shedding of 
the outgrown old shell, a sudden increase in size, and the 
gradual hardening of the shell newly formed. Kot only is 
the external skeleton cast off in the moult and the linings 
of the masticatory stomach, the esophagus, and intestine, 
but also the internal skeleton, which consists for the most 
part of a complicated linkwork of hard tendons to which 
muscles are attached." 






ARTHROPODS. CLASS CRUSTACEA 



111 



w? 



109. Peripatus (class Onychophora). — It is generally be- 
lieved that the Crustacea, insects, and spiders, together 
with their numerous relatives, trace their ancestry back to 
animals that bore a certain resemblance to the segmented 
worms. Most of these ancient types have fi 

long been extinct, but here and there % M 

throughout the earth we occasionally meet w^4 

with them. 

Among the most interesting of these 
are a few widely distributed species belong- 
ing to the genus Peripatus (Fig. 66), but as 
they are comparatively rare we shall dis- 
miss them with a very brief description. 
They usually dwell in warm countries, un- 
der rocks and decaying wood, emerging at 
night to feed on insects, w T hich they ensnare 
in the slime thrown out from the under 
surface of the head. Their external form, 
their excretory system, and various other 
organs are worm-like. On the other hand, 
the appendages are jointed, and one pair 
has been modified into jaws. The peculiar 
breathing organs characteristic of the in- 
sects are also present. Peripatus therefore 
gives us an interesting link between the 
worms and insects, and also affords an idea 
of the primitive insects from which the 
modern forms have descended. 

110. The centipeds and millipeds (class 
Myriapoda). — Many of the myriapods — that 
is, the centipeds and thousand-legged worms 
—are familiar objects under logs and stones 
throughout the United States. The first of these (Fig. 67) 
are active, savage creatures, devouring numbers of small 
animals, which they sting by means of poison-spines on the 
tips of the first pair of legs. The bite of the larger tropical 





Fig. G6.— Peripatus 
{Peripatus eiseni). 
Twice the natural 



112 



ANIMAL FORMS 



species especially causes painful but not fatal wounds in 



man. 



On the other hand, the millipeds (Fig. 68) or thousand- 
legs are cylindrical, slow-going animals, feeding on vegetable 



<l 




Fio. 67.— Centiped. 
One-half natural size. 



Fig. 68.— Thousand-legs or milliped {Julus). 
Natural size. 



substances without causing any particular damage, except in 
the case of the " cutworms," which often work great injury 
to crops. When disturbed they make little effort to escape, 
but roll into a coil and emit an offensive-smelling fluid, 
which renders them unpalatable to their enemies. 

All present a great resemblance to the segmented worms, 
as their popular names often testify ; but, on the other 
hand, many points in their organization indicate a closer 
relationship to the insects. As in the latter, the head is 
distinct, and bears a pair of antennae, the eyes, and two or 
three pairs of mouth-parts. The trunk is more worm-like, 
and consists of a number of similar segments, each bearing 



ARTHROPODS. CLASS CRUSTACEA 113 

one or two pairs of jointed legs. In their internal organ- 
ization the character of the various systems closely resem- 
bles that of the insects, and will be more conveniently 
described in that connection. 

Among the myriapods the females are usually larger 
than the males. Some of the centipeds deposit a little 
mass of eggs in cavities in the earth and then abandon 
them, while others wrap their bodies about them and pro- 
tect them until the young are hatched. The millipeds lay 
in the same situations, but usually plaster each egg over 
with a protective layer of mud. After several weeks the 
young appear, often like their parents in miniature, but in 
other species quite unlike, and requiring several molts to 
complete the resemblance. 



CHAPTER X 

ARTHROPODS {Continued). CLASS INSECTS 

111. Their numbers. — It has been estimated that upward 
of three hundred thousand named species of insects are 
known to the zoologist, and that these represent a fifth, or 
possibly a tenth, of those living throughout the world. Many 
of these species, as the may-flies and locusts, are represented 
by millions of individuals, which sometimes travelm such 
great swarms that they darken the sky. With nearly all 
of these the struggle for existence is fierce and unrelenting, 
and it is little wonder that such plastic animals have 
changed in past times and are now becoming modified in 
order to adapt themselves to new situations where food is 
more abundant and the conditions less severe. Owing to 
such modifications we find some species fitted for flying, 
others for running and leaping, or for a life underground, 
and many for a part or all of their lives are aquatic in their 
habits. 

112. External features. — The body of an insect— the 
grasshopper, for example — consists of a number of rings 
arranged end to end, as we have seen them in the Crustacea 
and the segmented worms. In the abdomen these are 
clearly distinct, but in the thorax, and especially the head, 
they have become so intimately united that their number 
is a matter of uncertainty. These three regions — head, 
thorax, and abdomen — are usually clearly defined in most 
insects, but they are modified in innumerable ways in ac- 
cordance with the animal's mode of life. 

114 






ARTHROPODS. CLASS INSECTS 115 

The head usually carries the eyes, a pair of feelers (an- 
tennae), and three pairs of mouth-parts which may be fash- 
ioned into a long, slender tube to be used in sucking, and 
frequently as a piercing organ ; or they may be constructed 
for cutting and biting. The thorax bears three pairs of 
legs and often one or two pairs of wings. The appendages 
of the abdomen are usually small and few in number, or 
even absent. 

113. Internal anatomy. — The restless activity of insects 
is proverbial. Some appear to be incessantly moving about, 
either on the wing or afoot, and are endowed with com- 
paratively great strength. Ants and beetles lift many times 
their own weight. Numerous insects are able to leap many 
times their own length, and others perform different kinds 
of work with a vigor and* rapidity unsurpassed by any other 
class of animals. As is to be expected, the muscular sys- 
tem is well developed, and exhibits a surprising degree of 
complexity. Over five hundred muscles are required for 
the various movements of our own bodies, but in some of 
the insects more than seven times this number exist. The 
amount of food necessary to supply this relatively immense 
system with the required nourishment is correspondingly 
large. Many insects, especially in an immature or larval 
condition, devour several times their own w r eight each day. 
Their food may consist of the juices of animals or plants, 
which they suck out, or of the firmer tissues, which are 
bitten or gnawed off. 

Xot only do the mouth-parts stand in direct relation to 
the habits of the animal and to its food, but, as w r e have 
often noticed before, the internal organization is also 
adapted for the digestion and distribution of the nutritive 
substances in the most economical way. For this reason 
we find the alimentary canal differing widely in the various 
forms of insects. In each case it extends from the mouth 
to the opposite end of the animal, and ordinarily consists 
of a number of different parts. In the insect shown in 



116 



ANIMAL FORMS 



^a/.c 



Fig. 69 the mouth soon leads into the esophagus, which 
in turn leads into the crop that serves to store up the food 
until ready for its entry into the stomach ; or in some of 
the ants, bees, and wasps it may contain material which 

may be disgorged and fed 
to the young. In many 
cases the stomach is small 
and ill-defined as in Fig. 69, 
and again it may reach 
enormous dimensions, near- 
ly filling the body. It may 
also bear numerous lobes or 
delicate hair-like processes, 
which afford a greater sur- 
face for the absorption of 
food. Behind the stomach 
are a number of slender 
outgrowths that are believed 
to act as kidneys. Beyond 
their insertion lies the in- 
testine, which, like the 
stomach, is the subject of 
many modifications in the 
different kinds of insects. 
The digested food is rap- 
idly absorbed through the coats of the stomach and intes- 
tine and enters a circulatory system which reminds us of 
what exists in many of the Crustacea. The heart is situ- 
ated above the digestive tract, and from it arteries pass out 
to different parts of the body. Here the blood leaves the 
vessels and is poured directly into the spaces among the 
viscera, whence it is finally conducted through irregular 
channels to the heart by its pulsations. 

In the Crustacea the blood is made to pass through a 
respiratory system usually in the form of definite gills, and 
the oxygen with which it is charged is distributed to all 




Fig. 69.— Cockroach, dissected to show ali- 
mentary canal, al. c— After IIatselek 
and Cori. 



ARTHROPODS. CLASS I XSK< ITS 1 1 7 

parts of the body. In the insects the blood serves almost 
entirely to carry the food, and the oxygen is conveyed 
through the animal by a remarkable contrivance found 
only in the insects, the spiders, and a few related forms. 

114. Respiratory system. — If we examine an insect, the 
grasshopper for example, Ave find a number of small brown 
spots on each side of the abdomen, each of which under a 
magnifving-glass is seen to be perforated by a narrow slit. 
Carefully opening the body, Ave find that each slit is in 
communication with a Avhite, glistening tube that rapidly 
branches and penetrates to all parts of the animal. When 
the body is expanded the air rushes into the outer openings, 
on through the open tubes, and is distributed with great 
rapidity to all the tissues of the body. In many insects 
some of these tubes connect with air-sacs which probably 
serve to buoy up the insect during its flights through 
the air. 

115. Wingless insects (Thysanura). — The simplest of all 
insects are the fishmoths and springtails, relatively small 
organisms covered with shining scales or hairs. The first 
of these is occasionally seen running about in houses feed- 
ing upon cloth and other substances, Avhile the latter live 
in damp places under stones and logs. They are without 
Avings, but are able to run rapidly and to leap considerable 
distances. In addition to the ordinary appendages, the 
abdomen bears Avhat are perhaps rudimentary legs, a fact 
which, together AAith their relatively simple structure, 
strengthens the belief that the insects have descended 
from centiped-like ancestors. 

116. Grasshoppers, crickets, katydids, etc. (Orthoptera). — 
Rising higher in the scale of insect life, AA r e arrive at the group 
of the cockroaches, crickets, grasshoppers, locusts, and 
other related insects. Four Avings are present, the first pair 
thickened and overlapping the second thinner pair. The 
latter are folded lengthwise like a fan, which is said to have 
given the name Orthoptera (meaning straight-Avinged) to 




118 ANIMAL FORMS 

this group of insects. These extend all over the world, 
being particularly abundant in the warmer countries, and 
their strong biting mouth-parts and voracious appetites 
render many of them dreaded pests to the farmer. The 
cockroaches are nocturnal in their habits, racing about at 
night, devouring victuals in the pantry and gnawing the 
bindings of books. During the day their flat bodies enable 
them to secrete themselves in crevices wherever there is 
sufficient moisture. 

In the grasshoppers, locusts, katydids, and crickets the 
body is more cylindrical, and the hind pair of legs are often 
greatly lengthened for leaping. The crickets and katydids 

are nocturnal, the former re- 
maining by day in burrows 
which they construct in the 
earth, the latter resting qui- 
etly in the trees. At night 

Fig. 70.— The Rocky Mountain locust.— J ° 

After Riley, from The Insect World. they least Upon vegetable 

matter principally, though 
some species are known to prey on small animals. Those 
insects we usually term grasshoppers (properly called lo- 
custs) are specially destructive to vegetation. Some spe- 
cies are strong fliers, and this, connected with their abil- 
ity to multiply rapidly, renders them greatly dreaded pests. 
They have been described as flying in great swarms, form- 
ing black clouds, even hiding the sun as far as the eye 
could reach. The noise made by their wings resembled 
the roar of a torrent, and when they settled upon the earth 
every vestige of leaf and delicate twig soon disappeared. 

The eggs of the majority of Orthoptera are laid in the 
ground, where they frequently remain through the winter. 
When hatched the young quite closely resemble the parents, 
and, after a relatively slight metamorphosis, assume the 
adult form. 

1 17. Dragon-flies, may-flies, white ants, etc. (Neuroptera). — 
The dragon-, caddis-, may-flies, ant lions, and the white ants 



ARTHROPODS. CLASS INSECTS 119 

possess four thin and membranous wings incapable of being 
folded. These possess a network of delicate nervures, giv- 
ing the name Xeuroptera (meaning nerve-winged) to the 
class. Of the forms mentioned above, all but the white 
ants lay their eggs in the water, and the developing larvae 




Fig. 71.— Dragon-fly (Libellula pulchella). 

spend their lives in this medium until the time comes for their 
complete metamorphosis into the adult. The larvae of the 
caddis-flies protect themselves within a tube of stones or sticks 
bound together with silken threads, which they usually 
attach to the under side of stones in running water. On 
the other hand, the young of the dragon- and may-flies, pro- 
vided with strong jaws, are active in the search of food and 
very voracious. In time they emerge from their larval skin 
and the water in which they live, and after a life spent on 
the wing they deposit their eggs and perish. The adult 
ant-lion, which has somewhat the appearance of a small 
dragon-fly, lays its eggs in light sandy soil. In this the 
resulting larvae excavate funnel-shaped pits, at the bottom 
of which they lie concealed. Insects stumbling into their 
9 



120 



ANIMAL FORMS 



pitfalls are pelted with sand, which the ant-lion throws at 
them with a jerky motion of the head, and are speedily 
tumbled down the shifting sides of the funnel to be seized 
and devoured. 

While the white ants are not in any way related to the 
true ants, they possess many similar habits. Associated in 
great companies, they excavate winding galleries in old logs 
and stumps, and, further, are most interesting because of 
the division of labor among the various members. The 
wingless forms are divided into the workers, which exca- 
vate, care for the young, and otherwise labor for the good 
of the others ; and into the soldiers, huge-headed forms. 



*< ; 



^ , 












Fig. 72.— Ant-lion larva plowing its way through the Band (upper figure) while an- 
other is commencing the excavation of a funnel-shaped pit similar to one on right. 
Photograph by A. L. Mklandek and C. T. Brues. 

whose strong jaws serve to protect the colony. The re- 
maining winged forms are the kings and queens. In the 
spring many of the royalty fly away from home, shed their 
wings, unite in pairs, and set about to organize a colony. 
The queen rapidly commences to develop eggs, and in some 



ARTHROPODS. CLASS INSECTS 



121 



species her body becomes so enormously distended with 
these that she loses the power of locomotion and requires 
to be fed. A single queen has been known to lay eggs at 
the rate of sixty per minute (eighty thousand a day), and 




Fig. 73.— Termites or white ants. a. queen ; b, winged male ; c, worker; d, soldier. 

those destined to royal rank are so nursed that they advance 
farther in their development than the remaining sterile 
and wingless forms. 

118. The bugs (Hemiptera). — The large and varied group 
of the bugs (Hemiptera) includes a number of semi-aquatic 
species, such as the water-boatmen, often seen rowing 
themselves along in the ponds by means of a pair of oar- 
shaped legs, in search of other insects. Somewhat similar 
at first sight are the back-swimmers, with like rowing 
habits, but unique in swimming back downward. Both of 
these bugs frequently float at the surface, and when about 
to undertake a subaquatic journey they may be seen to 
imprison a bubble of air to take along. Closely related are 
the giant water-bugs (Fig. 74), which often fly from pond 
to pond at night. In such flights they are frequently 



122 



ANIMAL FORMS 



attracted by lights, and have come to be called " electric- 
light bugs." 

Among our most dreaded insect pests are the chinch- 
bugs — small black-and-white insects, but traveling in com- 
panies aggregating many millions. 
As they go they feed upon the 
stems and leaves of grain, which 
they devour with extraordinary ra- 
pidity. The squash-bug family is 
also extensive, and destructive to 
the young squash and pumpkin 
plants in the early spring. 

The lice are small, curiously 
shaped bugs, w T hich suck the blood 
of other animals. The plant-lice, 
also small, suck the juices of 
plants, and are often exceedingly 
destructive. This is especially true 
of the phylloxera, a plant-louse 
which causes annually the loss of 
millions of dollars among the vine- 
yards of this and other countries. 
Even more destructive are tha scale-insects, curiously mod- 
ified forms, of which the wingless females may be found on 
almost any fruit-tree and on the plants in conservatories, 
their bodies covered with a downy, waxy, or other kind of 
covering, beneath which they remain and lay their eggs. 

119. The flies (Diptera). — The group of the Diptera 
(meaning two-winged) includes the gnats, mosquitoes, fleas, 
house-flies, horse-flies (Fig. 75), and a vast company of 
related forms. Only a single pair of wings is present, the 
second pair being rudimentary or fashioned into short, 
thread-like appendages known as balancers, though they 
probably act as sensory organs and are not directly con- 
cerned with flight. The mouth-parts are adapted for pier- 
cing and sucking. The eyes, constructed on the same plan 




Fig. 74.— Giant water-bug (Ser- 
phus dilatatus), with eggs at- 
tached. 



ARTHROPODS. CLASS INSECTS 



123 




Fig. 75.— Horse-fly (Therio- 
plectes). 



as those of the Crustacea, are comparatively large, and are 
frequently composed of a great number of simple eyes 
united together, upward of four 
thousand forming the eye of the 
common house-fly. 

These insects are widely distrib- 
uted throughout the world, where 
they inhabit woods, fields, or houses 
as best suits their needs. Their 
food is varied. Some suck the 
juices of plants, others attack ani- 
mals, and, while many are trouble- 
some pests, others, especially in the 
early stages of their existence, are 
of great benefit. 

120. Familiar examples. — Owing 
to the widely different habits and 
structure of the members of this group, we shall briefly 
consider two examples, the mosquito and the house-fly, 
which will give us a fairly good idea of the characteristics 
of all. The eggs of the mosquito are laid in sooty-look- 
ing masses on the surface of stagnant pools. Within a 
very short time the young hatch, and, owing to their pecul- 
iar swimming movements, are known as "wrigglers." They 
are then active scavengers, devouring vast quantities of 
noxious substances and performing a valued service. They 
frequently rise to the surface, take air into the tracheal 
system, which opens at the posterior end of the body, and 
descend again. After an increase in growth and many in- 
ternal changes resulting in a chrysalis-like stage, they rise 
to the surface, split the shell, and, using the latter as a float, 
carefully balance themselves and soon fly away. 

The house-fly usually lays its eggs in decaying vegetable 
matter, and the young, maggot-like in form, are active 
scavengers. They too undergo deep-seated changes during 
the next few days, finally transforming into the adult. 



124 



ANIMAL FORMS 



Many of this great group of the flies spend their early life 
in the water or other medium acting as scavengers ; but, on 
the other hand, numbers attack domestic and other animals, 
and throughout their entire lives are an intolerable plague. 
121. The beetles (Coleoptera).— Owing to the ease of pres- 
ervation and their bright colors, the beetles have probably 
been more widely collected than other insects. Fully ten 




Fig. 76. — Long-horned borer (Ergates). Larva (left-hand figure), pupa, and adult 

insect. 



thousand distinct species are known in Xorth America 
alone. They are all readily recognized by the two firm, 
horny sheaths enclosing the two membranous wings, which 
alone are organs of flight. The mouth is provided with 
jaws, which are used in gnawing. Some prey on noxious 
insects or upon decaying vegetable or animal matter, and 
are often highly beneficial ; but others attack our trees and 
domestic animals, and work incalculable damage. 



ARTHROPODS. CLASS INSECTS 125 

In some of the stag- or wood-beetles (Fig. 7G), which 
we may select as types, the adults are often found crawling 
about on or beneath the bark of trees, living on sap or 
small animals. The eggs laid in these situations develop 
into grub-like larvae, which bore their way through living 
or dead wood, and in this condition sometimes live four or 
rive years. They then transform into quiescent pupae (Fig. 
76), which finally burst their shells and emerge in the 
adult form. Others, like water-beetles and the whirligig- 
beetles, whose mazy motions are often seen on the surface 
of quiet streams, pass the larval period in the water. 
Under somewhat different conditions we find the potato- 
bugs, lady-bugs, fire-flies, and their' innumerable relatives, 
but the changes they undergo in becoming adult are essen- 
tially the same as those described for the other members of 
the order. 

122. The moths and butterflies (Lepidoptera). — The moths 
and butterflies occur all over the world. In their mature 




Fig. 77. — Monarch-bri\terfly {Anosia plexippvs). From photograph by A. L. Melan- 
der and C. T. Brues. 

state they are possessed of a grace of form and movement 
and a brilliancy of coloration that elicit our highest admi- 
ration. The mouth-parts are developed into a long pro- 
boscis, which may be unrolled and used to suck the nectar 
out of flowers, though in many of the adult moths, which 
never feed, it may remain unused. The wings, four in 
number, are covered with beautiful overlapping scales that 



126 



ANIMAL FORMS 



adhere to our fingers when handled. This feature, and 
the general plan of the body, which is much the same 




Flu. 78.— The silver-spot {Argynnis cybele). Photograph by A. L. Melander and 

C. T. Brues. 

throughout the group, enables us to recognize most of 
them at once. 

123. Development and metamorphosis. — In some of the 
simplest insects, as in the bugs, the young at birth resemble 
their parents. In other insects the resemblance is not so 
close. The young grasshopper, for example, hatches, from 
an egg laid in the ground, with a ridiculously large head 
and staring eyes ; still there is no difficulty in recognizing 
its relationships. During the next week internal changes 
take place. The shell is burst, and the grasshopper emerges, 
looking more like its parents than before. This process is 
repeated four or five times during the next few weeks, and 
the gradual changes thus produced finally bring the young 
insect to the adult form. This latter state has been attained 
by an incomplete metamorphosis. 



ARTHROPODS. CLASS INSECTS 



127 



In the flies, beetles, butterflies, and numerous insects 
the differences between the newly hatched young and the 
adult are vastly greater. No one looking on a caterpillar 
or a grub for the first time would suspect its origin, and 
the changes they undergo have attracted attention for cen- 
turies. Placing any of the ordinary caterpillars with their 
favorite food in a glass-covered box, we may readily watch 
their transformations. Provided with biting mouth-parts 
and a voracious appetite, they devour vast quantities of 
vegetation for several days. Finally they cease eating, and 



E ~ ~- 







Pig. 79.- 



-Life-history of silk-moth {Bombyx rnori). A, adult ; B, C. D, caterpillars of 
different ages ; E, F, G, silken cocoon and pupa ; H, eggs. 



suspend themselves head downward by means of a kind of 
cobweb. After remaining quiet a few hours, they burst 
their skin, and within appears a chrysalis or pupa. In the 
moths, for example, the silk-moth (Fig. 79), the caterpillar 
or silk-worm, after eating the favorite mulberry leaves, 
spins a silken cocoon, in which the pupa is produced. The 
larva? of beetles and many other insects excavate tunnels in 
wood or in the earth, and there undergo their transforma- 
tions. Invariably the pupa remains quiet for days, months, 



128 ANIMAL FORMS 

or even years, but when the proper time arrives the fully 
formed insect emerges, and takes to the wing. 

Wonderful internal changes have been taking place 
during this time. The organs fitted for the proper treat- 
ment of the vegetable food of the caterpillar or grub are 
destroyed, at least in part, and new systems are produced 
ready for the nectar and vegetable juices which are to be 
the food of the adult insect. All insects that pass through 
a pupal quiescent stage are said to undergo a complete 
metamorphosis. 

124. The ants, bees, wasps, etc. (Hymenoptera). — The ants, 
bees, and wasps are the best-known insects belonging to 
this order. They are characterized by four membranous 
wings, by biting and sucking mouth-parts, and the female 
is often provided with a sting. All undergo a complete 
metamorphosis. The eggs may be laid in the bodies of 
other insects, many of which are pests, and are thus de- 
stroyed ; or they may be deposited in the nests of other 
insects, the foster-parents being compelled to feed them; 
or they may be placed in marvelously constructed homes, 
and be the objects of the greatest attention, the parents or 
attendants often risking or losing their lives in their 
defense. The members of this order have long attracted 
attention, largely on account of their remarkable instinc- 
tive powers. They live in highly organized communities 
and certain of their characteristics may be illustrated by 
a study of some of the more familiar forms. 

125. The ants. — The ants live in communities consisting 
of anywhere from a dozen to many thousands of individuals, 
according to the species. Each of these colonies contains 
the queen, several young winged males and females, des- 
tined as kings and queens to found new colonies, and of a 
far greater number of wingless sterile females, the workers. 
The workers construct the greater part of the nest, which 
often consists of extensive galleries, nurseries, and grana- 
ries, excavated in wood or in the earth. They also attend 



ARTHROPODS. CLASS INSECTS 129 

to the acquisition of food, which consists of the sweet 
juices of plants, of other insects, or of leaves and seeds. 
These may be fed at once, or placed in storehouses until 
times of need. 

Certain species of ants make carefully planned attacks 
upon other weaker forms. The young are carried off, at 
times only after a prolonged and fierce struggle, and all 
are soon eaten, or a few may be allowed to develop and act 
as slaves. Some species are unable to exist without serv- 
ants, which feed them, wash them, and otherwise minister 
to their comfort. 

In some of their raids numerous plant-lice (delicate, 
usually green, insects, such as occur on our household 
plants) are often captured and carried into the nest. These 
so-called " ant-cows " are carefully tended, and in return 
yield up a tiny drop of a sugary fluid to the hungry ant 
that solicits it. 

The eggs laid by the queen develop into white worm- 
like creatures, which ordinarily spin cocoons when about to 
become pupae. These are incorrectly called " ant-eggs." 
Many, probably on account of insufficient nourishment, 
never develop reproductive organs. They become the neu- 
ters or workers. The winged royalty fly away from the 
colony, pair and found homes of their own, and become 
surrounded by a numerous progeny. 

126. The bees. — Among the bees we find a considerable 
number which lead solitary lives, excavating tunnels in 
earth or wood, as in the case of many of the wasps, but, 
unlike them, supplying the young with honey or pollen. 
Others may constitute a band of worthless insects which 
steal their food from their more industrious relations, in 
whose nests they also secretly deposit their eggs, leaving the 
young to be nourished with food rightly belonging to others. 

But it is with the social bees we are most familiar — the 
bumble- and honey-bees. The former usually build in the 
ground, and form colonies consisting of the queen and from 




130 ANIMAL FORMS 

twenty to two hundred workers. Eegular combs are not 
constructed, the young at first feeding on pollen masses or 
" bee-bread," and finally spinning cocoons. In the late 
summer males and females appear, but as winter comes on 
all perish except the queens, which seek a sheltered place, 
and in the spring revive to establish new colonies. 

In a wild state the honey-bees dwell in cavities of trees 
and other protected places, where they form colonies, 

consisting of the queen, of per- 
haps two hundred males or 
drones if the nest be examined 
in the spring and summer, and 
of a hundred times as many 
sterile females, the workers. 
These form among the most 
highly organized insect soci- 
eties known. All work for the 

Fig. 80.— Bumblebee {Bombus). 

good of the colony, lo each 
worker is assigned a definite task, which is never shirked. 
It must collect the honey, supply the wax for making the 
comb, take care of the brood, or in other ways minister to 
the welfare of the community. On the queen devolves 
the entire task of egg-laying. She may lay three thousand 
eggs a day and be fully occupied during the three or four 
years that she lives. The drones, or males, fertilize most 
of the eggs, and are then driven out from the hive, after 
a stay of a month or two. The eggs unfertilized by the 
drones are placed in large cells, and the young fed on 
pollen develop into males. The fertilized eggs may pro- 
duce queens or workers at the discretion of the queen. If 
the latter be desired, the eggs are placed in small cells with 
a scant amount of food, which apparently causes the repro- 
ductive system to remain undeveloped. The same eggs, if 
placed in the large queen cells and supplied with highly 
nutritious food, would have developed into queens. AY hen 
these latter appear they are vigorously attacked and killed 



ARTHROPODS. CLASS INSECTS 



131 



by the parent if not protected by the workers. If the 
young queen survive, the old queen departs with many of 
her subjects, and collects them into a dense swarm attached 
to a limb of a tree, where they remain until scouts return to 
conduct them to their new home. 

127. The wasps. — The digger-wasps are frequently to be 
seen gnawing tunnels in the wood or earth, at the inner end 




Fig. 81. 



-Nest of Vespa, & social wasp. Photograph by A. L. Melandek and 
C. T. Brues. 



of which an egg is laid. In some species the developing 
young is nourished by food carried in to it day by day. In 
other cases the parent may never see her child, dying or 
abandoning it before its birth ; but before departing she is 
careful to place within reach a sufficient supply of spiders, 
caterpillars, beetles, or locusts that shall nourish the little 
one until it becomes a motionless pupa. This stage is soon 
over, and the adult wasp now digs its way to the surface. 

Passing by the familiar mud-wasps or mud-dauber s, 
whose nests are common objects under stones or against 



132 ANIMAL FORMS 

the rafters of barns and houses, we arrive at the social 
wasps. As the name indicates, these insects, such as the 
yellow-jackets and hornets, live together in companies 
which consist, as in the ants and bees, of males, females, 
and workers. They also are fond of the juices of fruits, 
and many of them destroy insects which may be fed to the 
young. Their nests are variously situated and constructed, 
but all of them agree in being composed, at least in part, of 
a grayish substance which is in reality a kind of paper. 
With their jaws they scrape off from old logs and fences 
small particles of wood, which they probably mix with saliva, 
and rolling the mass into a ball set out for home. These 
pellets are then flattened out into thin sheets, and worked 
up into hexagonal cells, in which the eggs are laid. 

Along with the nests of the mud-daubers one frequently 
notices the nests of some of the familiar wasps {Polistes), 
which build cake-like nests composed of thirty or forty 
hexagonal cells attached by a stalk. Somewhat similar 
nests, though usually more extensive, are constructed by 
the yellow-jackets in cavities in the ground. The numer- 
ous combs of the hornet are surrounded by several sheets of 
wood-pulp, and the whole structure is attached generally 
to the limb of a tree. 

In the spring the nests of all these species of wasps are 
commenced by a single female, who has lived in a dormant 
condition through the winter. She builds a small nest and 
in time is surrounded by numerous workers, which live in 
perfect harmony, enlarging the nest and rearing the young. 
As autumn approaches the young males and females leave 
the nest ; but the males, together with the workers, all suc- 
cumb to the cold, and none but the females persist to found 
a new colony the following spring. 



CHAPTER XI 

ARTHROPODS (Continued). CLASS ARACHNID A 

1*28. General characters. — In this group, comprising the 
spiders, mites, and a large assemblage of related species, we 
again meet with great differences in form and structure 
which fit them for lives under widely different conditions. 
The three regions of the body, head, thorax, and abdomen, 
so clearly marked in the insects, are here less plainly do- 
fined. The head and thorax are usually closely united, and 
in the mites the boundaries of the abdomen are also indis- 
tinct. The appendages of the head are two in number, and 
probably correspond to the antennae and mandibles of other 
Arthropods. In the scorpions and some species of mites 
these are furnished with pincers for holding the prey, and 
in other forms they act as piercing organs. Usually the 
thorax bears four pairs of legs, a characteristic which readily 
separates such animals from the insects. 

The internal organization differs almost as much as does 
the external. In many species it shows a considerable re- 
semblance to that of some insects, but in others, especially 
those of parasitic habits, it departs widely from such a type. 
Respiration is affected by means of tracheae, or lung-books, 
which consist of sacs containing many blood-filled, leaf-like 
plates placed together like the leaves of a book. 

Usually, as in the insects, the young hatch from eggs 
which are laid, but in the scorpions and some of the mites 
the young develop within the body and at birth resemble 
the parent. Almost all of these organisms live either as 

133 



134 



ANIMAL FORMS 



parasites or as active predaceous animals upon other animals. 
For this purpose many are provided with keen senses for 
detecting their prey and poisonous spines for despatching it. 
129. The scorpions. — Owing to the stout investing armor, 
the strong pincers, and the general form of the body, the 
scorpions might at first sight be mistaken for near relatives 

of the crayfish or lobster. 
A more careful examina- 
tion will show that the 
two pairs of pincers prob- 
ably correspond to the 
antennae and mandibles of 
the Crustacea that have 
become modified for seiz- 
ing the food. The swol- 
len part of the animal 
lying behind the four 
pairs of legs is a part of 
the abdomen, of which 
the slender " tail " consti- 
tutes the remainder. On 
the tip of the tail is a 
curved spine supplied 
with poison glands. Sev- 
eral pairs of eyes are borne 
on the dorsal surface of 
the head and thorax, while 
on the under side of the animal several slit-like openings 
lead into as many small cavities containing the lung-books. 
The scorpions are the inhabitants of warm countries, 
where they may be found under sticks and stones through- 
out the day. At night they leave their homes in search of 
food, which consists chiefly of insects and spiders. These 
are seized by means of the pincers, and the sting is driven 
into them with speedily fatal results. It is doubtful if the 
poison causes death in man, but the sting of some of the 




Fig. 82.— Scorpion, showing pincer-like mouth- 
parts and spine-tipped tail. 



ARTHROPODS. CLASS ARACHN1DA 135 

larger species, which measure five or six inches in length, 
may produce certain disorders chiefly affecting the circula- 
tion. In this country there are upward of thirty species, 
most of which are comparatively small. 

130. The harvestmen. — The harvestmen or daddy-long- 
legs are small-bodied, long-legged creatures which resemble 
in general appearance several of the spiders. They differ 
from them, however, in the possession of claws correspond- 
ing to the smaller ones of the scorpion, and in their method 
of respiration, which is similar to that of insects. During 
the day they conceal themselves in dark crevices or stride 
slowly about in shaded places ; but at night they emerge 
into more open districts and capture small insects, from 
which they suck the juices. 

131. The spiders. — The spielers are world-wide in their 
distribution, and are a highly interesting group, owing 
chiefly to their peculiar habits. Examining any of our 
familiar species, it will be seen that the united head and 
thorax are separated by a narrow stalk from the usually 
distended abdomen. To the under side of the former are 
attached four pairs of long legs, a pair of feelers, and the 
powerful jaws supplied with poison-sacs, while eight shin- 
ing eyes are borne on the top of the head. On the abdo- 
men, behind the last pair of legs, are small openings into 
the lung cavities which contain a number of vascular, leaf- 
like projections known as lung-books. In some species 
a well-marked system of tracheae are also present. At the 
hinder end of the body are four or six little projections, 
the spinnerets, each of which is perforated with many 
holes. Through these the secretion from the glands be- 
neath is squeezed out in the form of excessively delicate 
threads, often several hundred in number, which harden on 
exposure to the air. According to the use for which these 
are intended, they may remain a tangled mass or become 
united into one firm thread ; and according to the habits 
of the animal, they may be used for enclosing their eggs, 

10 



136 



ANIMAL FORMS 



for lining their burrows, or for the construction of webs of 
the most diverse patterns. 

132. The habits of spiders.— Many species of spiders, some 
of which are familiar objects in fields and houses, construct 
sheets of cobweb with a tube at one side in which they may 





Fig. 83.— A tarantula-spider {Eurypelma lentzii). Natural size. Photograph by 
A. L. Melander and C. T. Brues. 

lie in wait for their prey or through which they may escape 
in times of danger. In the webs of the common orb- or 
wheel-weavers several radial lines are first constructed, and 
upon these the female spider spins a spiral web. Besting 
in the center of this or at the margin, with her foot on 
some of the radial threads, she is able to detect the slight- 
est tremor and at once to rush upon the entangled captive. 
Some of the bird-spiders and their allies, living in trop-^ 
ical America, and attaining a length of two inches, con- 
struct web-lined burrows in the ground. From these they 
stalk their prey, which consists of various insects and even 



ARTIIROPODS. CLASS ARACHNIDS 



137 



I 



small birds. These are almost instantly killed by the poison- 
fangs, and are then carried to the burrow, where the juices 
of the body are extracted. 

The trap-door spiders of the southwestern section of the 
United States also dig tunnels, which they cover with a 
closely fitting lid com- 
posed of earth. Eaising 
this they come out in 
search of insects, but if 
sought in turn, they dash 
into the burrow, closing 
the door after them, and 
holding it with such firm- 
ness that it is rarely forced 
open. If this should hap- 
pen, there are sometimes 
blind passage-ways, also 
closed with trap-doors, 
which usually baffle the 
pursuer. 

Finally, there are 
among the thousand spe- 
cies of spiders in the United States a considerable propor- 
tion which construct no definite web. Many of these may 
be seen darting about in the sunshine on old logs and 
fences, often trailing after them a thread which may sup- 
port them if they fall in their active leaping after in- 
sects. 

133. Breeding habits. — The male spiders are usually much 
smaller than the females, and some species are only one- 
fifteenth as long as the female and one one-hundredth of 
its weight. They are usually more brilliantly colored, more 
active in their movements, yet rarely spinning their own 
webs and capturing their own food, preferring to live at 
the expense of the female. At the breeding season the 
males of several species make a most interesting display 




Fig. 84.- 



-Trap-door spicier and burrow 
( Cteniza). 



138 



ANIMAL FORMS 



of their colors, activity, and gracefulness before the females ; 
and the latter, after watching these exhibitions, are said to 
select the one who has " shown off " in the most pleasing 
fashion. The life after this may be stormy, resulting in 
the death of the male ; but ordinarily the results are not 
so disastrous, and in a little while the female deposits her 
eggs in cases which she spins. In these the young develop, 
sometimes wintering here, and emerging in the spring to 
scamper about in search of food, or to drift through the 
air to more favorable spots on fluffy masses of cobweb. 

Few groups of animals are more interesting objects of 
study and more accessible. Their bites are rarely more 
serious than those of the mosquito — never fatal ; and a 
careful study of any species, however 
common, will undoubtedly bring to 
light many interesting and unknown 
facts. 

134. The mites and ticks. — The 
mites and ticks are the simplest and 
among the smallest of the animals 
belonging to this group. To the at- 
tentive observer they are rather com- 
mon objects, with homes in very dif- 
ferent situations. Some occur on liv- 
ing and decaying vegetation, in old 
flour and unrefined sugar, while oth- 
ers live in fresh water and a few in the sea. Almost all 
tend toward parasitism. Some of the insects which they 
pierce and destroy are a pest to man, but on the other hand 
some are intolerable owing to the diseases they produce. 
As to other parasitic organisms, degradation of structure 
manifest. The respiratory system, so important to the 




Fig. 85.— The itch-mite (Sar- 
copies scabei). 



IS 



active life of the insects, may be absent, the animal breath- 
ing through its skin. The circulatory system may be want- 
ing, the blood occupying spaces among the various organs 
being swept about by the animal's movements. And many 



ARTHROPODS. CLASS ARACIINIDA 



139 



other peculiarities have arisen which fit them for their 
different modes of life. 

135. The king crab (Limulus). — The king crab may be 
found crawling over the bottom or plowing its way through 
the sand and mud in many of the quiet bays from Maine 
to Florida. The large head and thorax of these animals 
are united into a horse- 
shoe-shaped piece, be- 
hind which lies the 
triangular abdomen. 
On the curved front 
surface of the former 
are a pair of small me- 
dian eyes, and farther 
outward are two larger 
compound ones. On 
the ventral side are 
six pairs of append- 
ages, instrumental in 
capturing and tearing 
the small animals that 
serve as food, and 
functioning in con- 
nection with the ter- 
minal spine as locomo- 
tor organs. On the 
ventral surface of the abdomen are numerous plate-like flaps 
which serve in respiration, and in the imperfect swimming 
movements in which these animals occasionally indulge. 

These relatively large and clumsy creatures are the rem- 
nant of a great number of strange, uncouth animals that in- 
habited the earth in past ages. Many of them show a close 
resemblance to the scorpions. The anatomy and develop- 
ment also show certain points of resemblance, and by some 
are thought to give us an idea of the ancient type of spider- 
like animal from which the modern forms have descended. 




Fig. 86.- 



-The king or horseshoe crab {Limulus 
polypfyemus). 



CHAPTEE XII 

ECHINODERMS 

136. General characters. — The division of the echino- 
derms includes the starfishes, sea-urchins, serpent- or brittle- 
stars, sea-cucumbers, and crinoids or sea-lilies. All are ma- 
rine forms, and constitute a conspicuous portion of the 
animals along almost any coast the world over. From 
these shallow-water situations they extend to the greatest 
depths of the ocean, and the bodily form possesses a great 
number of variations, adapting them to lives under such 
diverse conditions; and yet there is perhaps no group of 
organisms so clearly defined or exhibiting so close a resem- 
blance throughout. At one time it was thought that their 
radial symmetry was an indication of a close relationship 
to the coelenterates, but more careful study has shown them 
to be much more highly developed than this latter group, 
and widely separated from it. A skeleton is almost always 
present, consisting of a number of calcareous plates embed- 
ded in the body-wall, and often supporting numbers of pro- 
tective spines, which fact has given to the group the name 
Echinoderm, meaning hedgehog skin. 

137. External features.— The body of a starfish (Fig. 87) 
consists of a more or less clearly defined disk, from which 
the arms, usually five in number, radiate like the spokes 
of a wheel. At the center of the under side the mouth is 
located, and from it a deep groove, filled with a mass of 
tubular feet, extends to the tip of each arm. Innumerable 
calcareous plates firmly embedded in the body-wall serve 

140 



ECHINODERMS 



141 



for the protection of the internal organs, and at the same 
time admit of considerable movement. 

In the brittle-stars (Fig. 88) the central disk is much 
more sharply defined than in the preceding forms, and the 
long snake-like arms are capable of a very great freedom of 
movement, enabling the animal to glide over the sea-bottom, 
or through the crevices of the rocks, at a surprising rate. 

In several species, otherwise closely resembling those 




Fig. 87.— Starfish (Asterias ocracea), ventral view. One-half natural size. 

in Fig. 88, the arms divide repeatedly. These are the so- 
called basket-stars, living in the deeper waters of the sea, 
where they, like other brittle-stars, act as scavengers and 
devour large quantities of decomposing plant or animal 
remains. 

At first sight the globular spiny sea-urchins (Fig. 90) 
would scarcely be recognized as close relatives of the star- 
fishes. A closer examination, however, shows the mouth to 
be located on the under side of the body ; from it five rows 
of feet radiate and terminate close to the center of the 
dorsal side, and the arrangement of the plates forming the 



142 



ANIMAL FORMS 



skeleton indicate that the sea-urchin is comparable to a 
starfish, with its dorsal surface reduced to insignificant 
proportions. 

In the sea-urchins the calcareous plates possess a great 
regularity, and are so closely interlocked that they prevent 




Fig. 88.— Brittle- or serpent-stars (speeies undetermined). Natural size. 



any motion of the body-wall. Also, each plate is usually 
provided with highly developed spines, movable upon a ball- 
and-socket joint. These spines serve for locomotion, and, 
in some instances, for conveying food to the mouth. A 
considerable number of sea-urchins show an irregularity in 
form which destroys to a corresponding degree the radial 
symmetry. This is due to various causes, but especially to 
a compression of the body, which, in the "sand-dollars," 



ECI1IX0PERMS 



14? 



has resulted in the production of a thin, cake-like form 
(Fig. 91). 

If the spherical body of a sea-urchin were to be stretched 
in the direction of a line joining the mouth and the center 




Fig. 



-Basket-star {Astrophytori). One-half natural size. 



of the dorsal surface, a form resembling a sea-cucumber 
(Fig. 92) would be the result. These latter organisms live 
among crevices of the rocks, embedded in the mud or bur- 
rowing in the sand at the bottom of the sea. In such situa- 
tions they are well protected, and a highly developed skele- 
ton, such as that of the sea-urchin, would not only be of 
little value, but a positive hindrance to locomotion. The 
skeleton, therefore, is much reduced, consisting of a few 
scattered calcareous plates embedded in the fleshy body- 
wall. Another peculiar feature is almost universally pres- 
ent, in the form of a circlet of tentacles surrounding the 
mouth, which serve either for the purpose of respiration, 
for locomotion, or to convey food to the mouth. 

A very good imitation of the general plan of a sea-lily 
or crinoid (Fig. 93) could be made by attaching a serpent- 



144 



ANIMAL FORMS 



star, especially one of the basket-stars, by its dorsal side 
to a stalk. In the crinoids the numerous branches of the 

arms are compara- 
tively short, and in 
the arrangement of 
the internal organs 
there are numer- 
ous differences, but 
for all that the re- 
semblance of these 
organisms to the 
other echinoderms 
is undoubted. 

138. Haunts.— 
The greater num- 
ber of starfishes 
occur alongshore, 
slowly crawling 
about in search of 
food, or concealed 
in dark crevices of 
the rocks, where they may often be found as the tide goes 
out, and we know that in gradually lessening numbers other 
species lead similar lives at different levels far down in the 
dark and gloomy depths. In these same locations the sea- 
urchins occur, sometimes singly, but more usually associa- 
ted in great numbers, several species excavating hollows in 
the rocks, within which they obtain protection. The brit- 
tle-stars and sea-cucumbers may also be found occasionally 
in open view, but more often they make their way about in 
search of food buried in the sand. The crinoids are usual- 
ly inhabitants of deeper water, where they are found asso- 
ciated often in great numbers. A few species upon attain- 
ing the adult condition separate from the stalk, and are 
able to move about (Fig. 95), but the remaining species 
never shift their position. 




Fig. 90.— Sea-urchin {Strongylocentrotus purpuratus). 
Natural size. 



ECHIXODERMS 145 

139. The organs of defense and repair of injury. — As we 
have seen, the body-wall of the echinoderms is provided 
with a series of plates, often bearing spines which serve as 
organs of defense, and to protect the internal organs. The 
starfishes and sea-urchins also possess numerous modified 
spines (pedicellaria) scattered over the surface of the body, 
which have the form of miniature birds' beaks, fastened to 
slender muscular threads. During life these jaws continu- 
ally open and close, and it is said they clean the body of 
debris that settles on it ; but on the other hand there are 
several reasons for the belief that they also act as organs 
of defense. Thus protected, the natural enemies of echino- 
derms appear to be relatively few, and are confined chiefly 
to some of the fishes whose teeth are especially modified 
for crushing them. In this 
way, and owing to the action 
of the breakers, they suffer 
frequent injury, but many 
species exhibit to a remark- 
able degree the ability to re- 
generate lost parts. Experi- 
ments show that if all the 
arms of a starfish be separa- 
ted from the disk the latter 
will within two or three 
months renew the arms ; and FlG - ^l.-Sand-doiiar, a flat sea-urchin. 

, . . , „ Natural size. 

a single arm with a part of 

the disk is able to renew the missing portions in about the 

same length of time. 

The brittle-stars, as their name indicates, are usually ex- 
cessively delicate, often dropping all of their arms upon the 
slightest provocation ; but here again the ability is present 
to develop the lost portions. 

Sea-cucumbers resent rough treatment by vigorously 
contracting their muscular walls and removing from the 
body almost the entire digestive tract, the respiratory tree, 




146 



ANIMAL FORMS 



Hi 




and a portion of the locomotor system ; but some species, at 
least, renew them again. In some of the starfishes and 

brittle-stars portions of the body 
appear to be voluntarily de- 
tached and to develop into new 
individuals, and it is thought 
that such self-mutilation is a 
normal method of reproduction. 
140. Locomotor system. — One 
of the most characteristic and 
remarkable features of the echi- 
noderms is the water-vascular 
system, a series of vessels con- 
taining water which serve in the 
process of locomotion. Their 
arrangement and mode of opera- 
tion are, with slight modifica- 
tions, the same throughout the 
group, and may be readily un- 
derstood from their study in 
the starfish. 

On the dorsal surface of a 
starfish, in the angle between 
two of the arms, is a round, slightly elevated, calcareous 
plate, the madreporic body (Fig. 95, m./j.), which under 
the microscope appears full of holes, like the " rose " of a 
watering-pot. This connects with a tube that passes to 
the opposite side of the body, where it enters a canal 
completely encircling the mouth. On this ring-canal a 
number of sac-like reservoirs with muscular walls are at- 
tached, and from it a vessel extends along the under sur- 
face of each arm from base to tip. Each of these radial 
water-mains gives off numerous lateral branches that open 
out into small reservoirs similar to those located on the 
ring-canal, and a short distance beyond communicate 
through the wall of the body with one of the numerous 




Fig. 92.— Sea-cucumber {Cucu- 
maria sp.). Natural size. 



K( IIIXODERMS 



147 



tube-feet, which, as we have seen, are slender tubular or- 
gans, many in number, filling the grooves on the ventral 
surface of each arm. This entire system of tubes and 
reservoirs is full of water, taken in, it is said, through the 
perforated plate, and, when the starfish wishes to advance, 
many of the little reservoirs con- 
tract, forcing water into the cav- 
ity of the feet, with which they 
are in communication, thus ex- 
tending the extremity of the tubes 
a considerable distance. The 
terminal sucker of each foot, act- 
ing upon the same principle as 
those on the cuttlefish, attaches 
firmly to some foreign object, 
whereupon the muscles of the 
foot contract, drawing the body 
toward the point of attachment. 
This latter movement is similar 
to that of a boatman pulling him- 
self to land by means of a rope 
fastened to the shore. When the 
shortening of the tube-feet has 
ceased, the sucking disks release 
their attachment, project them- 
selves again, and this process is 
repeated over and over. At all 
times some of the feet are con- 
tracting, and a steady advance of 
the body is the result. 

This method of locomotion 
also obtains in the sea-urchins and cucumbers, but in the 
serpent-stars the tube-feet have become modified into feel- 
ers, and the animal moves, often rapidly, by means of twist- 
ing movements of the arms. The feet have this character 
also in the crinoids, where the animal is generally without 




% 



Fig. 93.— Sea-lih r or crinoid. 



148 



ANIMAL FORMS 




Fig. 94.- 



-An unattached crinoid (Antedon). One- 
half natural size. 



the power of locomotion. In some of the sea-cucumbers 
five equidistant rows of tube-feet extend from one end of 
the body to the other, and the animal crawls worm-like 
upon any side that happens to be down ; but certain spe- 
cies living in the sand, 
where tube - feet will 
not work satisfactorily, 
have lost all traces of 
them, and creep like an 
earthworm from place 
to place. In all the 
sea-cucumbers the feet, 
situated nearthe mouth, 
have been curiously 
modified to form a cir- 
clet of tentacles, which 
range in form from 
highly branched to short and thick structures, and in func- 
tion from respiratory organs and those of touch to con- 
trivances for scooping up sand and conveying it to the 
mouth. 

141. Food and digestive system. — In the echinoderms the 
body-wall is comparatively thin (Fig. 95), and encloses a 
great space, the body-cavity, in which the digestive and re- 
productive organs are contained. As the former in various 
species is adapted for acting upon very different kinds of 
food, it shows many modifications ; but there are a few prin- 
cipal types which may be briefly considered. 

In the starfishes the mouth enters almost directly into 
the cardiac division of the stomach, a capacious, thin-walled 
sac, much folded and packed away in the disk and bases of 
the arms (Fig. 95, b). This in turn leads into the second 
pyloric portion (<?), with thicker walls and dorsal, to the 
first, from which a short intestine leads to the exterior, 
near the center of the disk. Another conspicuous and im- 
portant feature is the so-called liver, consisting of a pair 



ECHINODERMS 149 

of closely branched, fluffy glands (?), extending the entire 
length of each arm and opening into the pyloric stomach. 

The starfishes are carnivorous and highly voracious, de- 
vouring large numbers of barnacles and mollusks which hap- 
pen in their path. If these are small and free they are 
taken directly into the stomach, but when one of relatively 
large size is encountered the starfish settles down upon it, 
and, slowly pushing the cardiac stomach through the mouth, 
envelops it in the folds. Digestive fluids are now poured 
over it, and the victim is speedily despatched and in a partly 
digested condition is gradually absorbed into the body, leav- 




Fig. 95.— Dissection of starfish to show : «, pyloric stomach ; b, bile-ducts (above), 
cardiac stomach (below) ; b.c, body-cavity ; /, feet ; g, spines ; i, intestine ; 
/, liver; m, mouth; m.p., madreporic plate; r, reservoir; r.c, ring canal; 
/.///., stomach retractor muscle ; ?\v., radial vessel ; s, stone canal ; t, respira- 
tory tree. 

ing the shell and other indigestible matters upon the exte- 
rior. Oysters and clams close their shells when thus attacked, 
but a steady, continuous pull on the part of the starfish 
finally opens them, and the stomach is spread over the fleshy 
portions with speedily fatal results. In the interior of the 
body the food is transferred to the pyloric stomach, sub- 
jected to the action of the liver, and when completely dis- 
solved is borne to all parts of the body. 



150 ANIMAL FORMS 

The digestive system of the starfishes, with its various 
subdivisions and appendages, is in some respects more com- 
plicated than in the other classes. This is most strikingly 
the case with the serpent-stars, where the entire system for 
disposing of the minute animals and plants on which it 
feeds consists of a simple sac communicating with the 
exterior by a single opening — the mouth. 

In the sea-cucumbers large quantities of sand are taken 
into the body, and the minute organisms and organic mat- 
ter are digested from it. In the sea-urchins the mouth is 
provided with five teeth, and the food consists of minute 
bits of seaweeds, which these snip off. Such diets evidently 
require a comparatively simple digestive apparatus, for in 
both it consists throughout its whole extent of a tube of 
equal caliber, in which the various divisions of esophagus, 
stomach, and intestine are little, if at all, defined. This 
is usually somewhat longer than the body, and therefore 
thrown into several loops ; and in the sea-cucumbers its last 
division is expanded and furnished with more highly mus- 
cular walls, which aid in respiration. 

142. Development. — With but a few exceptions, the eggs 
of the echinoderms are laid directly in the surrounding 
water, and for many days the exceedingly minute young 
are borne great distances in the tidal currents. During 
this period they show no resemblance to their parents, and 
only after undergoing remarkable transformations do they 
assume their permanent features. In every case they have 
a live-rayed form in early youth, but in several species of 
starfishes additional arms develop until there may be as 
many as twenty or thirty. 



CHAPTER XIII 

THE CHORDATES 

143. General characters. — Up to the present time we have 
been studying the representatives of a vast assemblage of 
animals whose skeletons, if they have any at all, are located 
on the outside of the body. In the corals, the mighty com- 
pany of arthropods, and the echinoderms, it is external. On 
the other hand, we shall find that the animals we are now 
about to consider, the fishes, frogs, lizards, birds, and mam- 
mals, are in possession of an internal skeleton. In some of 
the simpler fishes and in a number of more lowly forms (Fig. 
96) it is exceedingly simple, and consists merely of a gristle- 
like rod, the notochord (Fig. 98, nc), extending the length 
of the body and serving to support the nervous system, which 
is always dorsal. This is also the type of skeleton found in 
the young of the remaining higher animals, but as they grow 
older the notochord gives way to a more highly developed 
cartilaginous or bony, jointed skeleton, the vertebral column. 

In the young of all these back-boned or chordate ani- 
mals, the sides of the throat are invariably perforated to 
form a number of gill-slits. In the lower forms these per- 
sist and serve as respiratory organs, but in the higher ani- 
mals they disappear in the adult. The chordates are thus 
seen to be distinguished by the possession of a dorsal nerv- 
ous cord supported by an internal skeleton and by the 
presence of gill-slits, characters which separate them widely 
from all invertebrates. 

The chordates may be divided into ten classes, seven of 
11 151 



152 



ANIMAL FORMS 



which (the lancelets, lampreys, fishes, amphibians, reptiles, 
birds, and mammals) are true vertebrates, while the others 
embrace several peculiar animals of much simpler organiza- 
tion. 

144. The ascidians. — Among the latter are a number of 
remarkable species belonging to the class of ascidians or 

sea-squirts (Fig. 96). 
These are abundantly 
represented along our 
coasts, and are readily 
distinguished by their 
sac -like bodies, which 
are often attached at 
one end to shells or 
rocks. On the opposite 
' extremity two openings 
exist, through which a 
constant stream of water 
passes, bearing minute 
organisms serving as 
food. When disturbed 
they frequently expel 
the water from these 
pores with considerable 
force, whence the name 
" sea-squirt." While 
many lead solitary lives, 
numerous individuals of other species are often closely 
packed together in a jelly-like pad attached to the rocks, 
and others not distantly related are fitted to float on the 
surface of the sea. 

The young when hatched resemble small tadpoles both in 
their shape and in the arrangement of some of the more 
important systems of organs. For a few hours each swims 
about, then selecting a suitable spot settles down and ad- 
heres for life. From this point on degeneration ensues. 




Fig. 96.— Ascidian or sea-squirt. 



THE CHORD ATES 153 

The tail disappears, and with it the notochord and the 
greater part of the nervous system. The sense-organs van- 
ish, the pharynx becomes remodeled, and numerous other 
changes occur, leaving the animal in its adult condition, 
with little in its motionless, sac-like body to remind one of 
a vertebrate. 

145. The vertebrates. — Since the remainder of this vol- 
ume is concerned with the vertebrates it will be well at the 
outset to gain some knowledge of their more important 
characteristics. One of the most apparent is the presence 
of a jointed vertebral column, composed of cartilage or 
bone, which supports the nervous system. To it are also 
usually attached several pairs of ribs, two pairs of limbs, 
either fins, legs, or wings, and in front it terminates in a 
more or less highly developed skull. In the space par- 
tially enclosed by the ribs, the body-cavity, a digestive sys- 
tem is located, which consists of the stomach and intestine, 
together with the attached liver and pancreas. The cir- 
culatory system is also highly organized, and consists of a 
muscular heart, arteries, and veins which ramify through- 
out the body. Breathing, in the aquatic animals, is car- 
ried on by means of gills, and in the air-breathing forms 
by means of lungs, which, like the gills, effect the removal 
of carbonic-acid gas and the absorption of oxygen. The 
nervous system, consisting of the brain situated in the 
head and the spinal cord extending through the body 
above the back-bone, even in the lower vertebrates, is far 
more complex than in the invertebrates. The sense-organs 
also attain to a high degree of acuteness, and in connec- 
tion with the highly organized nervous system enable these 
forms to lead far more varied and complex lives than in 
any of the animals heretofore considered. 



CHAPTER XIV 

THE FISHES 

146. General characters. — In a general way the name fish 
is applied to all vertebrates which spend the whole of their 
life in the water, which undergo no retrograde metamor- 
phosis, and which do not develop fingers or toes. Of other 
aquatic chordafces or vertebrates the ascidians undergo a 
retrograde metamorphosis, losing the vertebral column, and 
with it all semblance of fish-like form. The amphibians, 
on the other hand, develop jointed limbs with fingers and 
toes, instead of paired fins with fin rays. A further com- 
parison of the animals called fishes reveals very great dif- 
ferences among them — differences of such extent that they 
cannot be placed in a single class. At least three great 
groups or classes must be recognized : the Lancelets, the 
Lampreys, and the True Fishes. The general characters of 
all these groups will be better understood after the study 
of some typical fish, that is one possessing as many fish-like 
features as possible, unmodified by peculiar habits. Such an 
example is found in the bass, trout, or perch. In either fish 
the pointed head is united, without any external sign of a 
neck, to the smooth, spindle-shaped body, which is thus fitted 
for easy and rapid cleaving of the water when propelled by 
the waving of the powerful tail (Fig. 97). A keel also has 
been provided, enabling the fish to steer true to its course. 
This consists of folds of skin arising along the middle line of 
the body, supported by numerous bony spines or cartilaginous 
154 



THE PISHES 155 

rays. These are the unpaired -fins, as distinguished from 
the paired ones, which correspond to the limbs of the higher 
vertebrates. In the bass or perch the latter are of much 
service in swimming, and are also most important organs in 
directing the course of the fish upward or downward, or for 




H 

Fig. 97.— Yellow perch (Perca jlavescens). df, dorsal fins ; pc. pectoral fin ; pf, pelvic 

fin ; v, ventral fin. 

aiding the tail in changing the course from side to side ; 
or they may be used to support the animal as it rests upon 
the bottom in wait for food ; and, finally, they may serve to 
keep the body suspended at a definite point. 

In addition to an internal skeleton the bass or perch, 
like the greater number of fishes, is more or less enclosed 
and protected by an external one, consisting of a beautifully 
arranged series of overlapping scales, which afford protec- 
tion to the underlying organs, and at the same time admit 
of great freedom of movement. These usually consist of a 
horny substance, to which lime is sometimes added, and 
are peculiar modifications of the skin, something like the 
feathers, nails, and hoofs of higher forms. 

147. The air-bladder. — Xaturally a fish's body is heavier 
than the water in which it lives, and there are reasons for 
thinking that the air-bladder (Fig. 106, a.U.) acts in the 



156 ANIMAL FORMS 

bass and perch and many other fishes as a float to enable 
them, without much effort, to remain suspended at a defi- 
nite level. By compressing this sac, partly by its own mus- 
cles and partly by those of the body-wall, the bulk of the 
fish is made less, and it sinks ; upon the relaxation of these 
same muscles the body expands and rises again. Deep-sea 
fishes, when brought to the surface, where the pressure is 
relatively slight, are found with their air-bladders so dis- 
tended that they can not sink again, and the float of surface 
fishes would be as useless if they were to be carried into the 
depths below, so that such fishes are compelled to keep 
within tolerably definite limits of depth. Morphologically 
considered, the air-bladder is a modified or degenerate lung, 
and in many fishes it is lost altogether. 

148. Respiration. — Looking down the throat of the perch 
or any other fish, a series of slits (the gill-openings), usually 
four or five in number, may be seen on each side communi- 
cating with the exterior. In the sharks these outer open- 
ings are readily seen, but in the bony fishes they open into 
a chamber on each side of the head, covered by a bony plate 
or gill-cover that is open behind. On raising these flaps 
the gills may be seen composed of great numbers of bright- 
red filaments attached to the bars between each slit. Dur- 
ing life the fish may be seen to open its mouth at regular 
intervals, and, after gulping in a quantity of water, to close 
it again, contracting the sides of the throat to force it out 
of the gill-openings and over the gill-filaments to the exte- 
rior. During this process the blood traversing the excess- 
ively thin filaments extracts the oxygen from the water and 
carries it to other parts of the body. 

With this information, let us return to the study of the 
three classes of fishes. 

149. The lancelet (Branchiostoma). — The lancelet, some- 
times called amphioxus (Fig. 98), the type of the class Lepto- 
cardii) is a little creature, half an inch to four inches long, in 
the different species, transparent and colorless, living in the 



THE FISHES 



157 



sand in warm seas, the nine species known being found in 
as many different regions. A lancelet may be regarded as 
a vertebrate reduced to its lowest terms. Instead of a 
jointed back-bone, it has a cartilaginous notochord, running 
from the head to the tail. A nervous cord lies above it, 
enclosed in a membranous sheath. No skull is present, and 
the nerve-cord does not swell into a brain. There are no 
eyes and no scales. The mouth is a vertical slit, without 
jaws. There is no trace of the shoulder-girdle (shoulder- 
blade and collar-bone) or pelvis (hip-bone) from which 




Fig. 98.— The California lancelet {BrancMostoma californiense). Twice the natural 
size, g, gills ; I, liver ; m, mouth ; n, nerve-cord ; nc, notochord. 

spring the paired fins, which, in true fishes, correspond to 
arms and legs. The circulatory system is fish-like, but there 
is no heart, the blood being driven about by the contraction 
of the walls of the vessels. Along the edge of the back and 
tail is a rudimentary fin, made of fin-rays connected by mem- 
brane. In the character and arrangement of its organs the 
lancelet is certainly like a fish, but in degree of develop- 
ment it differs more from the lowest fish than the fish does 
from a mammal. 

150. Lampreys (or Cyclostomes). — The class of lampreys 
stands next in development (Fig. 99). The notochord gives 
way anteriorly to a cartilaginous skull, in which is con- 
tained the brain, of the ordinary fish type. There are eyes, 
and the heart is developed, and consists of an auricle and 
a ventricle. As distinguished from the true fish, the lam- 
preys show no trace whatever of limbs or of the bones 
which would support them. The lower jaw is wholly want- 
ing, the mouth being a roundish sucking disk. The fins 



158 



ANIMAL FORMS 



are better developed, but of the same structure as in the 
lancelet. There is no bony matter in the skeleton, and 
there are no scales. The nasal opening is single on the top 
of the front of the head. 

There are about twenty-five species in this class. Some 
of them, called lampreys, ascend the streams from the sea 




Fig. 99. — Lampreys. 

in the spring for the purpose of spawning. The young 
undergo a metamorphosis, at first being blind and tooth- 
less. The adults feed mostly on the blood of fishes, which 
they suck after scraping a hole in the flesh with their rasp- 
like teeth. The others, called hag-fishes, live in the sea 
and bore into the bodies of other fishes, whose muscles they 
devour. All are slender, smooth, and eel-shaped. 

From their structure and a few fossil remains we sup- 
pose that these eel-like forms existed long ago, probably be- 
fore the more highly developed sharks and bony fishes made 
their appearance, but it is difficult to determine whether 
their simple organization is of such long standing or is not 
in part the result of semiparasitic habits, or a life spent 



THE PISHES 



159 



largely in burrowing. Like the lancelet and other simple 
chordates, they are of the greatest interest to the zoologist 
who gains from them some idea of the lowly vertebrate 
forms that peopled the earth long ago. 

151. True fishes. — The third class, Pisces or true fishes, 
to which the shark as well as the bass and perch belong has 
a well-developed skeleton, skull, and brain. The lower jaw 
is developed, forming a distinct mouth, and there is at least 
a shoulder-girdle and pelvis ; although the fins these should 
bear are not always developed, the general traits are those 
we associate with the fish. Of the true fishes, there are 
again several strongly marked groups, usually called sub- 
classes. Of these, three chiefly interest us. 

152. The sharks and skates. — Very early in the life of 
the sharks (Fig. 100) and skates (Selachii or Elasmobranchii) 




or \ 



Fig. 100.— Dogfish {Squalus acanthias). One-seventh natural size. 

a notochord appears, similar to that in the lancelet and the 
lampreys. As growth proceeds its sheath becomes broken 
up into a series of cartilaginous rings, which thus appear 
like spools strung on a cord. As the fish grows older these 
" spools " or vertebrae grow solid, cutting the notochord into 
little disks, and great flexibility is thus secured. Cartilagi- 
nous appendages also grow up and cover the spinal nerve- 
cord lying above, and give strength to the unpaired fins ; 
the paired fins also have their supports. The shoulder- 



160 ANIMAL FORMS 

girdle is placed behind the skull, leaving room for a distinct 
neck ; strong bars of cartilage bear the gills ; others form jaws 
to carry the teeth ; and a complex skull protects the brain 
and sense-organs, which are of a relatively high state of devel- 
opment. Throughout life the skeleton is of cartilage, with 
perhaps here and there a little bone where greater strength 
is required. Besides these, there are numerous minor 
characters which the student will readily find for himself. 

The sharks and skates or rays live chiefly in the sea, 
and some reach an enormous size, the largest of all fishes. 
Some are very ferocious and voracious ; others are very mild 
and weak, and the development of teeth is in direct pro- 
portion to their voracity of habit. In earlier geologic times 
there were many more species of them than now exist. 

153. The lung-fishes. — The lung-fishes (Dipnoi) are pe- 
culiar forms living in some of the rivers of Australia and 
the tropical regions of Africa and South America. In these 
the air-bladder is developed as a perfect lung. During the 
wet season they breathe like other fishes by means of gills, 
but as the rivers dry up they burrow into the wet mud and 
breathe by means of lungs which are spongy sacs of which 
the air-bladder of other fishes is a degenerate representative. 
As we shall see, they resemble in this respect the tadpoles 
and some adult Amphibia (frogs and salamanders). The 
paired fins are also peculiar in structure, having an elongate 
jointed axis, with a fringe of rays along its length, a struc- 
ture almost as much like that of the limbs of a frog as that 
of a fish's fin. In fact the Dipnoi must be regarded as an 
ancestral type, an ally of the generalized form from which 
Amphibia and bony fishes have descended. Only four liv- 
ing species of dipnoans are known, but great numbers of 
fossil species are found in the rocks. 

154. The bony fishes (Teleostei). — The bony fishes, or 
Teleosts, are distinguished by the bony skeleton, the sym- 
metrical tail, and by the development of the air-bladder as 
a more or less completely closed sac, useless in respiration. 



THE FISHES 161 

Often this organ is altogether wanting, as in the common 
mackerel. About ten thousand kinds of bony fishes are 
known. The species swarm in every sea, lake, or river 
throughout the earth, and some form or another among 
them is familiar to every boy in the land. These fishes arc 
divided into about two hundred families, and these may be 
arranged in fifteen to twenty orders. As these are mostly 
distinguished by features of the skeleton, we need not name 
them here. In Jordan and Evermann's Fishes of North and 
Middle America, as well as in various other books, the stu- 
dent of fishes can find the characters by which orders may 
be distinguished. 

155. Sturgeons and garpikes (Ganoidea). — While the great 
majority of the typical fishes possess a bony skeleton, there 
are a few quaint types — the ganoid fishes, snch as the stur- 
geons (Fig. 101) and garpikes — in which it is cartilaginous or 
partly bony. In past ages these were probably the highest 
type of fishes, and from their fossil remains we may con- 
clude that they flourished in vast numbers ; but at present 
they are almost extinct. In this country the ganoids are 
represented by several species, the best known being the 
sturgeons which inhabit the Great Lakes, the Mississippi, 
and its tributaries ; while on the East coast the common 
sturgeon (Acipenser sturio) often leaves the sea and ascends 
rivers. They are the largest fishes found in fresh water, 
attaining a length of ten or twelve feet, and a weight of 
five hundred pounds. Their food consists of small plants 
and animals, which they suck in through their tube-like 
mouth. The garpikes live in the larger lakes and rivers 
throughout the East and Mississippi Valley. Their bodies, 
from three to ten feet in length, according to the species, 
are covered with comparatively large regularly arranged 
square scales, and the upper jaw is elongated to form a 
kind of beak, abundantly supplied with teeth. They arc 
carnivorous, voracious fishes, working great havoc among 
the more defenseless food-fishes. 



THE FISHES 163 

15G. The catfishes. — Lowest of all the bony fishes we may- 
place the great group to which almost all fresh-water fishes 
belong. In this group the four vertebrae situated next the 
head are firmly united, and by means of certain small lever- 
like bones a connection is formed between the air-bladder 
and the ear of the fish, which is sunk deep in the skull. 
The air-bladder thus becomes a sounding organ in the 
function of hearing. The family of catfishes possesses this 
structure, and the student should look for it in the first one 
he catches. The catfishes are remarkable for the long feel- 
ers about the mouth, with which they pick their way on the 
bottom of a pond. There are many kinds the world over. 
The small ones are known as horned pout or bullhead. In 
these the dorsal and pectoral fins are armed each with a 
strong, sharp spine, which is set stiff when the fish is dis- 
turbed, and makes them very troublesome to handle. The 
catfishes have no scales. 

157. The carp-like fishes. — The still greater carp family 
includes all the carp, dace, minnows, and chubs. They 
have the air-bladder joined to the ear, just like the catfish, 
but they lack the long feelers and the fin spines, while the 
soft body is covered with scales, and there are no teeth in 
the mouth. In the throat are a few very large teeth, which 
the ingenious boy should find. In the sucker family these 
throat teeth are like the teeth of a comb, and the mouth is 
fitted for sucking small objects on the river bottom. 

158. The eels. — In the great order of eels the body is 
long and slim, scaleless, or nearly so, with no ventral fins. 
The shoulder-girdle has slipped back from the head, so as 
to leave a distinct neck, while ordinary fishes have none. 
Of eels there are very many kinds — some large and fierce, 
some small as an earthworm ; and one kind comes into fresh 
water. 

159. Herring and salmon. — In the great order which in- 
cludes the herring and salmon the vertebrae are all alike, 
the ventral fins far from the head, and the scales smooth to 



164 



ANIMAL FORMS 



the touch. The herring and shad are examples, as also the 
salmon and trout. Some live in the great depths of the 
sea, even live miles below the surface. These are very soft 
in body, being under tremendous pressure. They are inky 
black — for the sea at that depth seems black as ink — and 
most of them have luminous spots which give them light 
in the darkness. Some species have the forehead luminous, 
like the headlight of an engine. Most of these deep-sea 
fishes are very voracious, for there is nothing for them to 
feed on save their neighbors. 

160. The pike, sticklebacks, etc. — Several small orders 
stand between these soft-rayed, smooth-scaled fishes and 




Fig. 102.— The blindflsfa and its parentage. A, Dismal Swamp fish {ChoJog aster 
avetUS), the ancestor of (l>) Agassi/. 's cave fish {ChologOSter agOSSizi) and (V) 

cave blindfleh I TyphXtchthys subterram uti). 



the form, like the perch and bass, which has many spines in 
the dorsal fin. Among these transitional forms is the pike 
(Fig. UK)) — long, slender, circumspect, and voracious, lying 
in wait under a lily-pad ; the blindfish, which lost its eves 
through long living in the streams of the great caves; the 
stickleback, small, wiry, malicious, and destructive, steal- 
ing the eggs and nibbling the tins of any larger fish; the 
sea-horse, clinging with its tail head downward to floating 



166 ANIMAL FORMS 

seaweed, the male carrying the eggs about in his pocket 
until they hatch ; the mullet, stupid, blundering, feeding 
on minute plants, crushing them in a gizzard like that of 
a hen, but withal having soft flesh, good for the table ; the 
flying-fishes, which sail through the air with great swiftness 
to escape their enemies. 

161. The spiny-rayed fishes. — In the group of spiny- 
rayed fishes the ventral fins are brought forward and joined 
to the shoulder-girdle. The scales are generally rough to 
the touch, and the head is usually roughened also. There 
are many in every sea, ranging in size from the Everglade 
perch of Florida, an inch long, to the swordfish, which is 
thirty. These are the most specialized, the most fish-like 
of all the fishes. Leading families are the perch, in the 
fresh waters, the common yellow perch, familiar to all boys 
in the Northeastern States ; the darters, which are dwarf 
perches, beautifully colored and gracefully formed, living 
on the bottoms of swift rivers ; the sunfishes, with broad 
bodies and shining scales, thriving and nest-building in 
the quiet eddies; the sea-bass of many kinds, all valued for 
the table ; the mackerel tribe, mostly swimming in great 
schools from shore to shore. After these come the multi- 
tude of snappers, grunts, Aveakfishes, bluefishes, rose-fishes, 
valued as food. Then follow the gurnards, with bony 
heads; the sculpins, with heads armed with thorns, the 
small ones in the rivers most destructive to the eggs of 
trout ; and at the end of the long series a few families in 
which the spines once developed are lost again, and the 
fins have only soft and jointed rays. It is a curious law of 
development that when a structure is once highly special- 
ized it may lose its usefulness, at which point degeneration 
at once sets in. Among fishes of this type are the cod- 
fishes, with spindle-shaped bodies, and the flounders, with 
flat bodies. The flounders lie on the sand with one side 
down, and the head is so twisted that the eyes come out to- 
gether on the side that lies uppermost. This side is col- 




I 

l 



I 






12 



168 ANIMAL FORMS 

ored like the bottom — sand colored or brown or black — and 
the under side is white. When the flounder is first hatched, 
the eyes are on each side of the head, and the animal 
swims upright in the water like other fishes. But it soon 
rests on the bottom ; it turns to one side, and as the body- 
is turned over the lower eye begins to move over to the 
other side. Finally, we may close the series with the an- 
glers (Fig. 105), in which the first dorsal spine is trans- 
formed into a sort of fishing-pole with a bait at the end, 
which may sometimes serve to lure the little fishes, which are 
soon swallowed when once in reach of the capacious mouth. 

162. Internal anatomy. — A few fishes are vegetarians, but 
the greater number are carnivorous. Some swallow large 
quantities of sand of the sea-bottom and absorb from it the 
small organisms living there. Others are provided with 
beaks for nipping off corals and tube-dwelling worms. Huge 
plate-like teeth enable others to crush mollusks, sea-urchins, 
and crabs, and many are adapted for preying upon other 
fishes. The latter are often able to escape, owing to the 
presence of numerous spines, sometimes supplied with 
poison-glands; or their colors are protective, and a vast 
number of devices are present which enable them with 
some degree of surety to escape their enemies and capture 
food. 

Usually, without mastication, the food passes into the 
digestive tract (Fig. 106), which in the main resembles that 
of the squirrel, but varies considerably according to the 
nature of the food it is required to absorb. As in other 
animals, it is usually longer in the vegetable feeders. In 
most fishes the walls of the canal are pushed out at the 
junction of the stomach and intestine, to form numerous 
processes like so many glove-fingers (the pyloric cceca, Fig. 
106, py.c), which probably serve to increase the absorptive 
surface. The same result is obtained in other ways, chiefly 
by numerous folds of the lining of the canal. 

The blood-system is much more complex in the fishes 



THE FISHES 



169 



than in any of the invertebrates. It also differs in its gen- 
eral plan from that of most adult vertebrates, owing to the 
peculiar method of respiration. In almost every case the 




Fig. 105 —Angler or frogfish (Lophhts piscatorius). One-tenth natural size.— After 

Baskett. 

vessels returning from all parts of the body unite into one 
vein leading into the heart, which consists of only one 
auricle and ventricle (Fig. 106). From the heart the blood 



170 



ANIMAL FORMS 



is forced through the gills, with all their delicate filaments, 
and now, laden with oxygen and nutritious substances al- 
ready absorbed from the coats of the digestive tract, it 



optl 

ptyhlcrh 



kd p { "£i. imM 




dn."9*af 



Fig. 106.— Dissection of a bony fish, the trout (Salmo). a.U., air-bladder; an., anal 
opening; au., auricle; gl.st., gills; gul., Esophagus; int., intestine; kd., kidney ; 
lr,, liver ; l.ov., ovary; opt.L, brain ; pyx., pyloric coeca ; sp.c, spinal cord ; $pl., v 
spleen ; st., stomach ; v., ventricle. 

travels on to all parts of the body, continually unloading 
its cargo in needy districts and waste matters in the kid- 
neys before returning once more to the heart. 

163. The senses of fishes. — The habits of fishes indicate 
that they know considerable of what is going on in the 
outside world, and their well-developed sense-organs show 
the degree of their sensitiveness. A share of this informa- 
tion comes through the sense of touch, which is distributed 
all over the surface of the body, chiefly in the more ex- 
posed regions sometimes especially provided with fleshy 
feelers, like those on the chin of the catfish. 

The sense of smell appears to be fairly developed, as is 
that of hearing ; but there is no evidence of a sense of taste. 
A few fishes chew their food, and may possibly taste it, but 
there are others that swallow it whole, and in all there are 
relatively a few nerves going to the tongue or floor of the 
mouth. 



THE FISHES 171 

The eyes of most fishes are highly developed, and are of 
the greatest use at all times. Exceptions to the rule are 
found in certain species which live in caves or in the dark 
abysses of the ocean. In some of these the eyes have dis- 
appeared almost completely, and the sense of touch be- 
comes correspondingly more acute ; in other deep-sea forms 
they have grown to a large size, enabling them to distin- 
guish objects in the gloom, like the owls and other noc- 
turnal animals. Embedded in the skin of some of these 
deep-sea fishes, and certain nocturnal ones, are peculiar 
spots, composed of a glandular substance, which produces 
a bright glow like that of the fireflies. These may be located 
on the head or arranged in patterns over various parts of 
the body, and may serve to light the fish on its way and 
enable it to see its food to better advantage, or it may act 
as a lure to many fishes that become victims to their own 
curiosity. In those fishes which are active most of the 
time the eyes are located on the sides of the head, and in 
those which remain at or near the bottom they are turned 
toward the top ; in every case where they can be used to 
the best advantage. 

164. Breeding habits. — Among fishes the egg-laying time 
usually comes with the spring, when the males of several 
species become more resplendent, and sometimes engage 
in struggles for their respective mates. In others this 
ceremony is performed without show of hostility. Some 
make nests, while others lay their eggs loosely in the water. 

In all the salmon family the young fishes are born in 
the colder fresh-water rivers, and later make their way into 
the sea, where they spend the greater part of their lives. 
When the time comes for them to lay their eggs they 
migrate in great companies, and make their way hundreds, 
perhaps thousands, of miles to the rivers in which they 
spent their youth. Up these streams they rush in crowds, 
leaping waterfalls and rapids, and, dashed and battered on 
the rocks, many, and in some species all, die from injuries 



172 ANIMAL FORMS 

or exhaustion after the breeding season is passed. The 
eggs, like those of the chubs, suckers, sunfishes, and cat- 
fishes, are usually buried in shallow holes in the sand, and 
the males of most fishes keep a faithful watch oyer the 
young until they are able to live in safety. In some of 
the sticklebacks and several marine species elaborate nests 
are composed of grass or seaweeds ; some of the catfishes 
carry the eggs until they hatch in their mouths or else in 
folds of spongy skin on the under side of the body ; in the 
pipefishes and sea-horses a slender sac along the lower sur- 
face of the male acts as a brood-pouch, in which the female 
places the eggs to remain until developed ; and some fishes, 
such as the surf-fishes and a number of the sharks, bring 
forth their young alive. On the other hand, the young of 
many of the herrings, salmon, cod, perch, and numerous 
other fishes are abandoned at their birth, and fall a prey to 
many animals, even their parents often included. 

In the former cases, where the young are protected, on]y 
a relatively few eggs are produced: where they are aban- 
doned the female often lays many millions. In every case 
the number of eggs is in direct relation to the chances the 
young have of reaching maturity, a few out of each brood 
surviving to perpetuate the race. 

165. Development and past history. — The eggs of the 
higher bony fishes are usually small (one-tenth to one-third 
of an inch in diameter), and the young when they hatch 
are accordingly little ; in the sharks the eggs are larger, 
the size of a hen's egg or even larger, and the young when 
born are relatively large and powerful. These differences, 
however, do not greatly affect the early development, for 
in every case the head and then the trunk soon become 
formed, gills arise, the nervous system appears, which is 
invariably supported by a skeleton in the form of a gristly 
rod — the notochord. In the lower forms of fishes this per- 
sists throughout life ; but in the sharks and skates it be- 
comes replaced in the adult by another and higher type of 



THE FISHES 173 

skeleton, which is much more specialized with the bony 
fishes. 

Those who study the fossils on the rocks tell us that 
the first fishes were very simple, and many believe that 
their skeleton, like that of the little growing fish, consisted 
only of a notochord. Many of these old forms died out 
long ago, while others gradually changed in one way and 
another to adapt themselves to their surroundings, the con- 
stant need of adaptation having resulted in the multitude 
of present-day types. Some, such as the lamprey, have 
probably changed relatively only to a slight extent ; others, 
like the sharks and skates, are much more altered; and 
the bony fishes are far from their original low estate, 
though their development has been rather toward a greater 
specialization for aquatic life than an advance upward. 
The little fish in its growth from the egg thus repeats the 
history of its ancestral development ; but as though in 
haste to reach the adult condition, it omits many impor- 
tant details. Moreover, the record in the rocks is not 
complete, and we have many things yet to learn of the 
ancient fishes and their development from age to age to 
the present day. 



CHAPTER XV 



THE AMPHIBIANS 



Ln" many respects the amphibians — toads, frogs, and sala- 
manders — resemble the fishes, especially the lung-fishes 
(Dipnoi). The modern amphibians are essentially fishes 
in their early life, but in developing legs and otherwise 
changing their bodily form they become adapted for a life 
on land under conditions differing from those of the fishes. 
Judging from this class of facts, we may assume that fish- 
like ancestors, by the development of the lungs, became 
fitted for a life on land, and that from these the amphib- 
ians of our times have been derived. 

166. Development. — The eggs of the Amphibia are laid 
during the spring months in fresh-water streams and ponds. 
They are globular, about as large as shot, and are embedded 
in a gelatinous envelope (Fig. 10T). They are either de- 
posited singly or in clumps, or festooned in long strings over 
the water-weeds. During the next few days development 
proceeds rapidly under favorable conditions, resulting in an 
elongated body with simple head and tail. In this condition 
they are hatched as tadpoles. As yet they are blind and 
mouthless, but lips and horny jaws soon appear, along with 
highly developed eyes. ears, and nose. External Huffy gills 
arise on the sides of the head, and slits form in the walls of 
the throat, between which gills are attached, and over which 
folds of skin develop, as in the fishes. A fin-fold like that 
of the lancelet or lamprey appears on the tail. The brain 
and spinal cord, extending along the line of the back, are 
supported by a gristly notochord, and complete and com- 
174 



THE AMPHIBIANS 



175 



plex internal organs adapt the animal to a free-swimming 
existence for days to come. 

The tadpole is now, to all intents and purposes, a fiVu — 
a fact most clearly recognized in its form, method of loco- 




Fig. 107.— Metamorphosis of the toad.— Partly after Gage, from Animal L 

motion, the arrangement of the gills, and the general plan 
of the circulatory system. 

16T. Further growth. — In the course of the next few- 
weeks hind limbs develop beneath the skin, through which 
they finally protrude. In the same manner, fore limbs arise 
at a later date. In position these organs are like the paired 
fins of fishes, but they are intended for crawling or leaping 
on land, and are modified in accordance with this need. As 
in the higher vertebrates, the limbs develop as arms and 
gs, with long fingers and toes, between which are stretched 
webs of skin, which serve in swimming. 



176 ANIMAL FORMS 

In the meantime large internal changes are also taking 
place. The wall of the esophagus has gradually pouched 
out to form the lungs. They are richly supplied with blood- 
vessels, closely resembling in their general features the 
lungs of the lung-fishes. The animal now rises to the sur- 
face occasionally to gulp in air, and it also continues to 
breathe by means of gills. At this stage of its existence, 
therefore, the larva is amphibious (two-living), and we have 
the interesting example of an animal extracting oxygen 
from both the water and the air. The diet of the tadpole 
at this time changes from vegetable to animal substances, 
and horny teeth give way to the small teeth of the frog, 
and the digestive system undergoes an entire remodeling 
to adapt it to its new duties. The young amphibian — 
whether frog, toad, or salamander — is now a four-legged 
creature, with well-developed head and tail, with lungs and 
gills, though the latter are usually fast disappearing, and is 
rapidly assuming those characters which will fit it for a 
terrestrial or semiaquatic existence. 

168. The salamanders. — The changes which now ensue in 
such a larva in reaching the adult condition are relatively 
slight in the lower salamanders. The external gills often 
persist (Fig. 110), the lungs are also functional, and the 
changes are largely those of increase of size. In the larger 
number of species the gills disappear more or less com- 
pletely (Fig. 108), such species often abandoning the water 
for homes in damp soil or under stones and logs, returning 
to it only when the time comes for their eggs to be laid. 
The limbs are always relatively weak, never supporting the 
body from the ground, but serving in a clumsy way to push 
it from place to place. In the aquatic forms the tail con- 
tinues to serve as a swimming organ. In some species the 
hind legs become rudimentary, or even entirely lacking. 
A still further modification occurs in a few burrowing spe- 
cies, which move by wrigglings of the body, and are with- 
out either pairs of legs. 



THE AMPHIBIANS 



177 



In geological times many of the salamanders were of 
great size, several feet in length, and some were enclosed 
in an armor consisting of bony plates. All now living have 
the skin naked, and with the exception of the giant species 
of Japan, three feet in length, and a few similar forms in 
America, the modern representatives are comparatively 




Fig. 108.— Blunt-nosed salamander {Amblystoma o])acum). Photograph by W. H. 

Fisher. 

feeble and measure their length by inches. Only a few, on 
account of their bright colors, are particularly attractive, 
while the others are usually shunned and considered re- 
pulsive, chiefly because of their supposed poisonous char- 
acter, though in reality few animals are more harmless. 

169. Tailless forms. — In the frogs and toads the meta- 
morphosis which the young undergo is almost as profound 
as that which takes place with the insects. The gills, to- 
gether with their blood-vessels, disappear completely. The 
tail, with its muscles, nerve-supply, and skeleton, is ab- 
sorbed. The cartilaginous notochord gives way to a jointed 
back-bone. A skull is developed ; numerous bones form in 
the limbs, affording an attachment for the powerful muscles 
which make the toad, and especially the frog, expert swim- 



178 ANIMAL FORMS 

mers and leapers, and thus equipped they hereafter lead a 
wholly terrestrial or serniaquatic life. 

170. Distribution and common forms. — All the Amphibia 
are dependent upon moisture. Almost all are hatched and 
developed in fresh water, and those which leave the water 
return to it during the breeding season. So we find repre- 
sentatives of the group all over the world having much the 
same range as the fresh-water fishes. The great majority 
of the salamanders are confined to the northern hemisphere, 
but the toads and frogs are almost universally distributed. 

Among the salamanders in this country only a relatively 
few species completely retain their external gills. This is 
the case with sirens and mud-puppies or water-dogs (Fig. 
110), which may occasionally be seen in the clear waters 
of our lakes and rivers crawling slowly about in search of 
food, and every now and then rising to the surface to gulp 
in air. The remainder lose their gills more or less com- 
pletely, and usually leave the water for damp haunts on 
land. One of the blunt-nosed salamanders, known as the 
tiger salamander (Arnhlystoma tigrinum), is found in moist 
localities in most parts of the United States. Besides these 
are numerous small species, among them the newts (Die- 
myctylus), ranging widely over the United States, living 
under logs and stones and feeding upon the small insects 
and worms inhabiting such situations. In several species 
of salamanders the lungs disappear with age, and respira- 
tion is performed solely through the surface of the skin. 

The tailless amphibians are much more abundant and 
familiar objects than the salamanders, and from the open- 
ing of spring until late in the fall they are met with on 
every hand. With few exceptions the frogs live in or about 
ponds and marshes, in which they obtain protection in 
troublous times and from which they derive the store of 
worms and insects that serve as food. On the other hand, 
the tree-frogs, as their name indicates, usually abandon the 
water and repair to moist situations in trees and other vege- 



THE AMPHIBIANS 1 7 ( .> 

tation. Their shrill, cricket-like calls are often heard in 
the summer. The fingers and toes are more or less dilated 
into disks at their tips, enabling them to climb with con- 
siderable facility; and they are further adapted to their 
surroundings on account of their protective colors. The 
toads undergo their metamorphosis while very small, and 
approach only the water at the breeding season. During 
the day they remain concealed in holes and crevices, but at 
the approach of evening come out in search of food. 

171. Means of defense. — The food of the members of this 
group consists chiefly of small fishes, insect larvae, snails, 
and little crustaceans, wdiich are swallowed whole. On the 
other hand, many Amphibia prey on each other, while most 
of them are eagerly sought by birds and fishes. Some, as 
the toads, stalk their food only during the night-time or 
depend upon their agility to escape their enemies. Others 
are colored protectively, the markings of the skin resem- 
bling the foliage of the earth upon which they rest, and in 
some species, as the tree-toads, this color-pattern changes 
as the animal shifts its position. A few species are most 
brilliantly colored with red, green, yellow, or combinations 
of these, in striking contrast to their surroundings. They 
have apparently few 7 enemies, possibly because of an un- 
pleasant odor or taste, and it has been suggested that their 
gorgeous tints are danger-signals, warning their w r ould-be 
captors from attempting a second time to devour them. At 
the same time it is well known that the somber-hued toads 
emit a milky secretion from the warty protuberance of 
their skin which is intensely bitter, irritating to delicate 
skin, and poisonous to several animals. 

172. Skeleton. — As in all vertebrates, the skeleton of the 
amphibian first arises as a cartilaginous rod, the notochord, 
which is afterward replaced by a jointed back-bone, to 
which the limbs are attached. The back-bone is anteriorly 
modified into a flat, usually complex, skull. In the sala- 
manders the number of vertebrae is sometimes very large, 



180 



ANIMAL FORMS 



and the body correspondingly long and snake-like ; but in 
other cases parts of the vertebrae are reduced in number, 
and the body is rather short and thick. In the frogs and 
toads this reduction reaches its culmination, for only nine 
distinct vertebrae are present, the tail vertebrae, correspond- 
ing to those of the salamanders, being represented by a 
rod-like bone, the urostyle, made of segments grown to- 
gether. 

173. Digestive and other systems. — In its main characters 
the digestive tract of the amphibian (Fig. 109) resembles 



apov.d tfdtf 0%k d0ii0. 



ur. anovd! 
^^sLapur. 



p.nd. 




Fig. 109.— Dissection of toad (Bnfo). an., anal opening; an., auricle; bl., bladder; 
duo., duodenum ; big., lung ; lr., liver; pn., pancreas ; ret., rectum ; spl., spleen; 
St., stomach ; v., ventricle. 

that of the fishes and the squirrel. The mouth is usually 
large, and the teeth are very small, as in the frog or sala- 
mander, or are lacking completely, as in the common toad. 
In many salamanders the tongue, like that of a fish, is fixed 
and incapable of movement. In most of the frogs and 
toads it is attached to the front of the mouth, leaving its 
hinder portion free, and capable of being thrown over and 
outward for a considerable distance. In the throat region 
gill-clefts may persist, but they usually close as the lungs 
reach their development. The succeeding portions of the 
canal are comparatively straight in the elongated forms, or 



THE AMPHIBIANS 181 

more or less coiled in the shorter species. In some cases 
no well-marked stomach exists, but ordinarily the different 
portions, as they are shown in Fig. 109, are well defined. 

As noted above, the circulation, in the tadpole is the 
same as in fishes, then lungs arise, and for a time respi- 
ration is effected both by gills and lungs, and the cir- 
culation resembles in its essential points that of the 
lung-fishes. This may continue throughout life, but more 
frequently the gills and their vessels disappear, and the 
circulation approaches that of the reptiles. In such forms 
the heart consists of two auricles and one ventricle. Into 
the left auricle pours the pure blood from the lungs ; into 
the right the impure blood from the body. To some 
extent these mix as they are forced into the general cir- 
culation by the single ventricle. The amount of oxygen 
carried is therefore smaller than in the higher air-breathers, 
the amount of energy is proportionately less, and hence it 
is that all are cold-blooded and of comparatively sluggish 
habits. 

In some species of salamanders the lungs may also dis- 
appear, and breathing is carried on by the skin, as it is to 
a certain extent in all amphibians. In the frogs and toads 
lungs are invariably present, and vocal organs are situated 
at the opening of the windpipe in the throat. These pro- 
duce the characteristic croaking or shrilling, which in many 
species are intensified through the agency of one or two 
large sacs communicating with the mouth-cavity. 

Although the brain is small in the amphibians, it is 
more complex in several respects than it is in fishes. 
The eyes are also usually well developed, but in some of 
the cave and burrowing salamanders they are concealed 
beneath the skin, and are rudimentary. The ear varies 
considerably in complexity in the different species, but in 
the possession of semicircular canals and labyrinth resem- 
bles that of the fishes. In the frogs and toads, as one may 
readily discover, the drum or tympanum is external, ap- 



182 



ANIMAL FORMS 



pearing as a smooth circular area behind the eye. Organs 
of touch, smell, and taste are likewise developed in varying 
degree of perfection. 

174. Breeding-habits. — While the great majority of am- 
phibians mate in the spring and deposit their eggs in the 
water, often to the accompaniments of croakings and pip- 
ings almost deafening in intensity, several species, for 
various reasons, have adopted different methods. Some of 
the salamanders bring forth young alive, and several species 
of toads and frogs are known in which the young are cared 
for by the parent until their metamorphosis is complete. 
In one of the European toads (Alytes) the male winds 
the strings of eggs about his body until the tadpoles are 







Fig. 110.— Salamanders. The 
axolotl (the larva of Am- 
bly stoma tigrinum) and 
the newt (Diemyetyhis to- 
rosvs). 



ready to hatch ; and in a few species of tree-toads the eggs 
are stored in a great pouch on the back of the parent until 
the early stages of growth are over. In the Surinam toad 
of South America the eggs are placed by the male on the 
back of the female, and each sinks into a cavity in the 
spongy skin. Here they pass through the tadpole stage 
without the usual attendant dangers, and emerge with the 
form of the adult. 



THE AMPHIBIANS 1S3 

Sunlight and warmth are apparent necessities for speedy 
development. Tadpoles kept in captivity where the con- 
ditions are generally unfavorable may require years to as- 
sume the adult form. As mentioned above, the tiger sala- 
mander (Ambly stoma tigrinum) occurs in most parts of the 
United States and Mexico. In the East this species drops its 
gills in early life as other salamanders do, and assumes the 
adult form, but in the cold water of high mountain lakes, 
in Colorado and neighboring States, it may never become 
adult, always remaining as in Fig. 110. This peculiar form 
is locally known as axolotl. In this condition it breeds. It 
is thus one of the very few examples of animals whose un- 
developed larvae are able to produce their kind. Owing to 
this trait it was at first considered a distinct species, and 
many years elapsed before its relationship to the true adult 
form was discovered. 



13 



OHAPTEB XVI 

THE REPTILES 

175. General characteristics. — In all the reptiles the gen- 
eral shape of the body, and to some extent the internal 
plan, is not materially different from that seen among the 
amphibians. In spite of external resemblance the actual 
relationship is not very close. It appears to be true that 
ages ago the ancestors of the modern reptiles were aquatic 
animals, possibly somewhat similar to some of the sala- 
manders ; but they have become greatly changed, and 
are now, strictly speaking, land animals. At no time in 
their development after leaving the egg do we find them 
living in the water and breathing by gills. Some species, 
such as the turtles, lead aquatic or semiaquatic lives, but 
the modifications which fit them for such an existence 
render them only slightly different from their land-inhabit- 
ing relatives. The skin bears overlapping scales or horny 
plates, united edge to edge, as in the turtles, enabling them 
to withstand the attacks of enemies and the effects of heat 
and dryness. Indeed, it is when heat is greatest that rep- 
tiles are most active. In no other class of vertebrates, and 
very few invertebrates, do normal activities of the body 
appear to be so directly dependent upon external warmth. 
In the presence of cold they rapidly grow sluggish, arid 
sink into a dormant state. 

As in the case of all animals, habits depend upon 
structure, and accordingly among the reptiles we find 
many remarkable modifications, enabling them to lead 
184 



THE REPTILES 



1S5 



widely different lives. Xevertheless all are constructed 
upon much the same plan. 

176. The lizards (Sauria).— As in the amphibians, es- 
pecially the salamanders, the body (Fig. Ill) consists of 
a relatively small head united by a neck to the trunks, 




Fig. 111.— Common lizard or swift {Sceloporus undulatus). Photograph by W. H. 

Fisher. 

which, in turn, passes insensibly into a tail, usually of con- 
siderable length. Two pairs of limbs are almost always 
present, and these exhibit the same skeletal structure as 
in the amphibians ; but in their construction, as in the 
other divisions of the body, we note a grace of propor- 
tion and muscular development which enable the lizards 
to execute their movements with an almost lightning-like 
rapidity. The mouth is large and slit-like, well armed with 
teeth, and the eyes and ears are keen. Scales of various 



186 ANIMAL FORMS 

forms and sizes, always of definite arrangement, cover the 
body. The scales are always colored, in some species as 
brilliantly as the feathers of birds, and usually harmonize 
with the surroundings of the animal, enabling it to escape 
the attacks of its many enemies. Altogether the lizards 
are a very attractive group of animals. As in the salaman- 
ders, the vertebral column is usually of considerable length, 
but it too presents a lighter appearance and a greater flexi- 
bility. Slender ribs are present, and a breast-bone and the 
girdles which support the limbs. Although more ossified 
than in the amphibians, the skull still continues to be com- 
posed here and there of cartilage. The roof also is yet 
incomplete, but with the firm plates on the surface of the 
head ample protection is afforded the small brain under- 
neath. As above mentioned, the limbs are slender and 
insufficient to support the body, which accordingly rests 
upon the ground, and by its wrigglings and the pushing of 
the limbs is borne from place to place. It will be recalled 
that some of the salamanders living in subterranean haunts 
and burrowing in the soil have no need of limbs, and the 
latter have accordingly disappeared. This condition is 
paralleled by certain species of lizards. The blindworms 
(which are neither blind nor worms, but true lizards, though 
snake-like in appearance) are devoid of limbs, as are also 
the " glass-snakes." In some species the hinder pair arise 
in early life, but they remain small, and ultimately disap- 
pear. In almost all lizards the tail is very brittle, breaking 
at a slight touch. In such case the lost member will grow 
again after a time. 

177. The snakes (Serpentes).— The snakes are character- 
ized by a cylindrical, generally greatly elongated body, in 
which the divisions into head, neck, trunk, and tail are not 
sharply defined. As we have seen, this is also true of cer- 
tain lizards, but the naturalist finds no difficulty in detecting 
the differences between them. Another peculiarity of the 
snakes is in the great freedom of movement of the bones 



THE REPTILES 



187 



not concerned with the protection of the brain. In the 
reptiles the lower jaw does not unite directly with the 
skull, as in the higher animals, but to an intermediate 
bone, the quadrate, which is attached to the skull. In the 
snakes these unions are made by means of elastic liga- 
ments. The two halves of the lower jaw are also held 




>*5 




Fig. 112.— Blacksnake (Bascanion constrictor). Photograph by W. H. Fisher. 

together by a similar band, so that the entire palate and 
lower jaw are loosely hung together. This enables the 
snake to distend its mouth and throat to an extraordinary 
degree, and to swallow frogs and toads but slightly smaller 
than itself. Where the prey is of relatively small size, the 
halves of the lower jaw alternate with each other in pulling 
backward, thus drawing the food down the throat. The 
food is never masticated. The teeth are usually small and 
recurved, and serve only to hold the food until it may be 
swallowed. The latter process is facilitated by the copious 
secretion of the salivary glands, which become very active 
at this time. 

A further character of the snakes is the absence exter- 



188 ANIMAL FORMS 

nally of any trace of limbs. However, in some of the 
pythons and boas hind limbs are present in the form of 
small groups of bones embedded beneath the skin and ter- 
minating in a claw. There thus appears to be no doubt 
that the ancestors of the modern snakes were four-footed, 
lizard-like creatures, which have assumed the present form 
in response to the necessity of adaptation to new conditions. 

More than any other order of vertebrates do the snakes 
deserve the name of creeping things, and yet their method 
of locomotion enables them to crawl and swim with a ra- 
pidity equal to that of many of the more highly developed 
animals. This depends chiefly upon certain peculiarities 
of the skeleton, which consists merely of a skull, vertebral 
column, and ribs. The vertebrae, usually two or three hun- 
dred in number, are united together by ball-and-socket 
joints, and each attaches by similar joints a pair of slender 
ribs. These in turn are attached to the broad outer plates 
upon which the body rests, and the whole system is operated 
by a powerful set of muscles. Upon the contraction of the 
muscles the ventral plates are made to strike backward 
upon the ground or other rough surface, which drives the 
body forward. Also, the ribs may be made to move back- 
ward and forward, and the snake thus progresses like a 
centiped or "thousand-legs." 

178. The turtles (Chelonia). — In many respects the tur- 
tles are the most highly modified of all the reptiles. The 
body (Fig. 113) is short and wide and enclosed in a shell or 
heavy armor, consisting of an upper portion, the carapace, 
and a flat ventral plate, the plastron. The shape of the 
carapace varies greatly from a low, flat shield to a highly 
vaulted dome, remaining cartilaginous throughout life, as 
in the soft-shelled turtles, or becoming bony and of great 
strength. These two portions of the shell form a box-like 
armor, through whose openings the head, tail, and limbs 
may be extended. The latter organs are superficially unlike 
those of any other order of animals. The head is generally 



THE REPTILES 



189 



thick-set and muscular, and provided with horny jaws 
entirely destitute of teeth, like those of the birds. The 
limbs also are usually short and thick and variously shaped, 
and adapted for aquatic or terrestrial locomotion. The 
number of vertebrae in the body and tail are relatively few, 
and the thick and heavy body is devoid of the elements of 
grace and agility of movement characteristic of the other 
reptiles. On the other hand, the former enjoy a freedom 
from the attacks of enemies not accorded to animals in 
general. 

At first sight the appearance of a turtle does not indi- 
cate a close relationship to the other reptiles, but a more 




Fig. 113.— Box-turtle (Terrapene Carolina). 

careful examination, and especially of their development, 
discloses a remarkable resemblance. The head, tail, and 
limbs are essentially similar to those of the lizards, but in 
the trunk region peculiar modifications have taken place. 
The ribs at first separate, as in other animals, flatten 
greatly, and unite with a number of bones embedded in 
the skin, thus forming one great plate overlying the back 
of the animal. About the circumference of the shield 
other dermal or skin-bones are added, which increase the 
area of the carapace, and at the same time still others have 



190 ANIMAL FORMS 

arisen and united on the ventral surface to form the plas- 
tron. In this process the shoulder- and hip-girdles which 
attach the limbs come to be withdrawn into the body, and 
we have the curious example of an animal enclosed within 
its back-bone and ribs. This is even more the case with 
the box-turtles (Fig. 113), common in the eastern United 
States, whose ventral plate is hinged so that after the 
limbs, head, and tail have been withdrawn it may be made 
to act like a lid to completely enclose the fleshy parts of 
the body. 

Scales and horny plates are present, as in other reptiles, 
the former covering all parts of the body except the cara- 
pace and plastron, which support the plates. In nearly all 
species the latter are of considerable size, and in the tor- 
toise-shell turtles are valuable articles of commerce. They 
also are sculptured in a fashion characteristic of each spe- 
cies, and may, like the colors of other animals, render them 
more like their surroundings, and consequently incon- 
spicuous. 

179. Crocodiles and alligators (Crocodilia). — The alligators 
(Fig. 114) and crocodiles are much more complex in struc- 
ture than the lizards, though their general form is much the 
same. The body is covered with an armor of thick bony 
shields and horny scales. These, along the median line, are 
keeled, and extending along the length of the laterally com- 
pressed tail form an efficient swimming organ and rudder. 
The mouth is of large size, and is bounteously supplied with 
large conical teeth, which are set in sockets in the jaw, and 
not fused with it, as in many of the lizards. The nose and 
ears may be closed by valves to prevent the entrance of 
water, and a similar structure blocks its passage beyond 
the throat while the mouth is open. When large animals, 
such as hogs or calves, are captured as they come to drink, 
these devices enable the alligator or crocodile to sink with 
them to the bottom and hold them until drowned. The 
limbs, short and powerful, are efficient organs of locomo- 



THE REPTILES 



191 



tion on land, and together with the general shape of the 
body, are also well adapted for swimming. 




Fig. 114.— Alligator {Alligator mississippiensis). 

180. Distribution of the lizards. — In a general way the 
number of reptiles is greatest where the temperature is 
highest. The tropics therefore abound in species, often 
of large size, and usually of bright coloration. As one 
travels northward the numbers rapidly diminish, their size 
is smaller, and the tints less pronounced. In all probability 
not less than four thousand known reptiles exist, whose 
haunts are of the most varied description. 

In Xorth America the lizards are almost exclusively 
confined to the southern portions, only a very few species 
extending up to the fortieth parallel. Among these the 
skinks (Eumeces) are most widely distributed. The blue- 
tailed skink is probably the most familiar, a small lizard 
eight or ten inches in length, dark green with yellowish 
streaks and a bright-blue tail. On sunny days it may 
sometimes be seen darting about on the bark of trees in 
search of insects, upon which it feeds. 

One of the most familiar lizards in this country is the 
"glass-snake," found burrowing in the drier soil of the 
southern half of the United States east of the Mississippi. 



192 



ANIMAL FORMS 



Both pairs of limbs are absent, but by wriggling movements 
of the body this lizard is able to force its way through light 
soil with considerable rapidity. It is a matter of some 
difficulty to secure entire specimens, for with other than 
the gentlest handling the tail severs its connection with 
the body, as the vertebrae in this portion are extremely 
brittle. This peculiarity, together with its shape, has given 
it the popular name of glass-snake. Many species of liz- 
ards will thus detach the tail, a habit which is a means of 
protection, enabling the animal to scamper away into a 
place of safety while its enemy is concerning itself with 
the detached member. Later on a new tail develops, 
though usually of a less symmetrical form. 

181. Horned toads. — The horned toads (Plirynosoma) are 
lizards peculiar to the hot, sandy deserts and plains of 




Fig. 115. — Gila monster {Heloderma suspectum). One-third natural size. 

Mexico and the western United States. The body is com- 
paratively broad and flat, almost toad-like, and is covered 
with scales and spines of brownish and dusky tint, so like 
dried sticks and cactus spines in form and color as to ren- 
der them difficult of detection. In captivity they readily 



THE REPTILES 193 

adapt themselves to their new surroundings, become tame, 
and feast on flies, ants, and other insects, which they cap- 
ture by the aid of their long tongue. The horned toads 
are perfectly harmless creatures, but when irritated some- 
times perform the remarkable feat of spurting a stream of 
blood from the eye toward the intruding object for a dis- 
tance of several inches. This has been regarded by some 
as a zoological fable ; but there are many who have watched 
the horned toad in its natural state and in captivity, and 
they assure us that it is a fact. 

In the hot deserts of Arizona and Sonora is another 
peculiar species of lizard known as the Gila monster (Helo- 
derma) (Fig. 115), having the distinction of being the only 
poisonous lizard known. Further protection is afforded 
by bony tubercles on the head and by scales over the 
remainder of the body, all of which are colored brown or 
various shades of yellow, giving the animal a peculiar 
streaked and blotched appearance. 

182. Distribution of the snakes. — The snakes are much 
more common than the lizards. All over the United States 
one meets with them, especially the garter- or water-snakes. 
Of less wide distribution are the black-, grass-, and milk- 
snakes, and a number of less known species, all of which 
are perfectly harmless and often make interesting pets. 
Some of them when cornered show considerable temper, 
flatten the head and hiss violently, and imitate j)oisonous 
forms, but venomous snakes are comparatively few in num- 
ber in northern and eastern United States. In the south- 
ern portions of the country they become more abundant. 
Along the streams and in the swamps the copperheads, and 
especially the water-moccasins, often lie in wait for frogs 
and fish. Both these species are especially dreaded, as they 
strike without giving any warning sound, but the name 
and bad reputation of the moccasin is often, especially in 
the South, transferred to perfectly harmless water-snakes. 
On higher ground are the rattlesnakes (Crotalus), once 



194 



ANIMAL FORMS 



abundant but now in many regions well-nigh exterminated. 
In these species the tail terminates in a series of horny 




Fig. lib.— Diamond-rattlesnake (Crotalus adamanteus). Photograph by W. H. 

Fisher. 

rings that produce a buzzing sound like that of the locust 
when the tail is rapidly vibrated. 

183. Distribution of the turtles. — The turtles are perhaps 
somewhat less dependent upon warmth than other reptiles, 
yet they too delight to bask in the sunshine, and soon grow 
sluggish in its absence. In all our fresh-water streams and 
ponds they are familiar objects, and several species extend 
up into Canada. Among the turtles the soft shell, the 
painted and the snapping turtles have the widest distri- 
bution, scarcely a good-sized stream or pond from the Gulf 
of Mexico to Canada, and even farther north, being without 
one or more representatives. All are carnivorous and vora- 
cious, and the snapping turtles are especially ferocious, and 
"for their size are the strongest of reptiles/' In the woods 
and meadows the wood-tortoise and box-turtles are occa- 



THE REPTILES 



L9£ 



sionally met with, and at sea several turtles exist, some of 
them of great Bize. Among these is the leather-turtle, 
found in the warmer waters of the Atlantic, lazily floating 
at the surface or actively engaged in capturing food. They 
attain a length of from six to eight feet, and a weight of 
over a thousand pounds, and are sometimes captured for 
food when they come ashore to bury their eggs in the sand. 
By this same method the loggerheads, the hawkbills, and 
the common green turtles are also captured in consider- 
able numbers. These are of smaller size, and the second 
named is of considerable value, as the horny plates cover- 




Fig. 117.— Hawkbill turtle {Eretmochelys imbricata). 



ing the shell furnish the tortoise-shell of commerce. These 
plates are removed after the animal is killed, by soaking 
in warm water or by the application of heat. 

184. Food and digestive system. — Some reptiles, among 
which are a number of species of lizards and the box- and 
green turtles, are vegetarians, but the great majority are 



196 



ANIMAL FORMS 



carnivorous, and usually very voracious. The lizards espe- 
cially devour large quantities of insects and snails, together 
with small fishes and frogs. The latter figure largely in 
the turtle's bill of fare, and in that of the snakes, which 
also capture birds and mammals. On the other hand, many 
of the reptiles prey upon one another ; and they are the 
favorite food of hawks and owls and numerous water-birds, 
of skunks and weasels and many other animals, which look 
for them continually. Many of the turtles, owing to their 
protective armor, and the snakes because of their poison- 
ous bite or great size and strength, are more or less ex- 
empt, but this is not true of their eggs and young. The 
smaller species depend upon keenness of sense, agility, and 
inconspicuous tints. These latter may undergo changes 
according to the character of the surroundings, but usually 
only to a slight extent. The chameleons of the tropics 
and a similarly colored green lizard on the pine-trees in 
the Southern States are able to change with great rapidity 
from green, through various shades, to brown. 

185. Respiration and circulation. — While still in the egg 
the young lizard develops rudimentary gills, and thus bears 



eai]A m( pr IJ % ^ImdrnM kd. 
^ 9 



r* an. 



Fig. 118.— Dissection of lizard (Sceloporus). an., anal opening ; au., auricle ; crb.h., 
brain ; coec, intestine ; kd., kidney ; Ling., left lung ; It., liver ; pn., pancreas ; 
sp.c. spinal cord ; spl., spleen ; st.. stomach ; v., ventricle of heart. 



evidence to the fact that its distant ancestors were aquatic ; 
but before hatching they disappear, and lungs arise, which 



THE REPTILES 197 

remain functional throughout life. Corresponding to the 
shape of the body, these are usually much elongated and 
ordinarily paired (Fig. 118, Ling.). The snakes are peculiar 
in having the left lung rudimentary or even lacking com- 
pletely, while the right one becomes greatly elongated and 
extends far back into the body. In nearly all the reptiles 
the amount of oxygen brought into the lungs is relatively 
large and the activity of the animal is proportionately 
great. The circulation of reptiles shows an advance be- 
yond that of the Amphibia. As in the latter, there are 
two distinct auricles ; but the chief difference arises from 
the fact that the ventricle is more or less divided by a par- 
tition which to a considerable degree prevents the blood 
returning from the lungs from mixing with the impure 
blood as it returns from its journey over the body. In the 
crocodiles and alligators the partition is complete, and the 
circulation thus approaches close to that of the higher 
animals. 

186. Hibernation. — Attention has already been called to 
the fact that reptiles are very susceptible to cold, rapidly 
growing less active as the temperature lowers. When win- 
ter comes on they seek protected spots, and either alone 
or grouped together hibernate. The various activities of 
the body during this period are at very low ebb. The blood 
barely circulates, breathing is imperceptible, and stiff 
and insensible to the world about them they remain until 
the warmth again stirs them to their former activity. 
Some of our common turtles must also pass a somewhat 
similar sleep while embedded far down in the mud during 
the disappearance of the ponds in summer. At such times 
no food is taken, but owing to their loss in weight it is 
probable that a slow consumption of the body supplies the 
small amount of necessary energy. 

187. Nervous system and sense-organs. — At first sight one 
is struck with the small size of the brain of fishes, Am- 
phibia, and reptiles. Their intelligence likewise is at low 



198 ANIMAL FORMS 

ebb. Almost all the movements and operations of the body 
appear to be carried on by the animal with little apparent 
thought. Their acts, like most of the animals below them, 
are said t6 be instinctive ; yet they are sufficiently well done 
to enable the animal to Jwocure its food, avoid its enemies, 
and lead a successful life. As is true of other animals, the 
ability of the reptile to cope with its surroundings depends 
to a great pxtent upon the keenness of one or all of its or- 
gans of special sense. In the reptiles the sense of sight is 
perhaps sharpest, but there is considerable variation in this 
respect. Eyelids are present in all except the snakes, to- 
gether with a third, known as the nictitating membrane, a 
thin, transparent fold located at the inner angle of the eye, 
over which it is drawn with great rapidity. In the snakes 
eyelids are absent, giving the eye its characteristic stare. 
Furthermore, their sense of sight, except in a few tree-dwell- 
ing species, appears to be defective, the majority depending 
largely upon the sense of touch. 

In all the vertebrates a very peculiar organ known 
as the pineal gland or 1 eye is situated on the roof of the 
brain. In several lizards its position is indicated by a trans- 
parent area in one of the plates of the head, and by an 
opening in the bones of the roof of the skull. In young 
reptiles, and especially in one of the New Zealand lizards 
(Hatteria, Fig. 119), its resemblance to an eye is decidedly 
striking. Lens, retina, pigment, cornea, are all present 
much as they are in some of the snails, but they finally 
degenerate more or less as the animal reaches maturity. 
It is a general belief that it represents the remnant of an 
organ of sight, a third eye, which looked out through the 
roof of the skull in some of the ancient vertebrates. 

With the possible exception of the few species of reptiles 
which produce sounds, probably to attract their mate, the 
sense of hearing is not particularly well developed. The 
senses of smell and taste are also comparatively feeble. The 
latter sense is located in the tongue, which is also popularly 



THE REPTILES 199 

supposed to serve for the purpose of defense, and that it is 
in some way related to the poison-glands. This, however, 
is an error. The tongue is used primarily as an organ of 




1 




Fig. 119. — Tnatera (Sphenodon piutctatus)-. 

touch, and in snakes especially it is almost continually 
darted in and out to determine the character of the animal's 
surroundings. 

188. Egg-laying, — The eggs of the reptiles are relatively 
large and enclosed in a shell like a bird's egg^ the shell, 
however, being leathery rather than made of lime. These 
are deposited in some warm situation, and generally left to 
themselves to hatch. Under stones, logs, and leaves, or 
buried lightly in the soil, are the positions most frequently 
chosen by the lizards and snakes. The turtles almost inva- 
riably select the warm sand at the edge of the water, and 
after scooping a hole lay several perfectly spherical eggs, 
usually at night. The alligators lay upward of a hundred 
eggs about the size of those of a goose, and guard them 
jealously until and even after they hatch. On the other 
hand, the young of many lizards and snakes are born alive, 
the eggs being hatched within the body. 

Many reptiles are surprisingly slow in attaining maturity, 
and live to an age attained by few other animals. It is a 
well-known fact that turtles live fully a hundred years, and 
14 



200 ANIMAL FORMS 

probably the same is true of the crocodiles and alligators 
and some of the larger snakes. Their enemies are few, and 
death usually results when the natural course is run. 

Throughout life all reptiles periodically shed their skin, 
as birds do their feathers and mammals their fur. In the 
snakes and some of the lizards the skin at the lips loosens, 
and the animal gradually slips out of its old slough, bright 
and glossy in the new one which previously developed. In 
the others the old skin hangs on in tatters, gradually com- 
ing away as they scamper through the grass. 









CHAPTEE XVII 

THE BIRDS 

189. Characteristics. — Birds form one of the most sharp- 
ly defined classes in the animal kingdom, and the variations 
among the different species are relatively small. " The 
ostrich or emu and the raven, for example, which may be 
said to stand at opposite ends of the series, present no such 
anatomical differences as may be found between a common 
lizard and a chameleon, or between a turtle and a tortoise/' 
and these we know to be relatively slight. 

In many respects the birds resemble the reptiles, and 
long ago in the world's history the relationship was much 
closer than now, as we know from certain fossil remains in 
this country and in Europe. One of the earliest of these 
fossil birds, that of the Archseopteryx, is a most remarkable 
combination of bird and lizard. Unlike any modern bird, 
the jaws were provided with many conical reptile-like teeth. 
The wings were rather small, and the fingers, tipped with 
claws, were distinct, not grown together, as in modern birds. 
The tail was as long as the body, and many-jointed, like a 
lizard's, each vertebra carrying two long feathers. The 
bird was about the size of a crow, and it probably could 
not fly far. Other ancient types have been discovered — 
principally sea-birds — many of which existed when the 
Pacific extended over the region now occupied by the 
Rocky Mountains. These were all of the same generalized 
type, intermediate between reptile and bird. This fact 
leads us to the belief that birds descended from reptilian 

201 



202 ANIMAL FORMS 

ancestors, and in becoming more perfectly adapted for an 
aerial life have developed into our modern forms. 

In the modern birds the most important peculiarities, 
those which separate them from all other animals, are 
correlated with the power of flight. The body is spindle- 
shaped, for readily cleaving the air. The fore limbs serve 
as wings. The hind limbs, supporting the weight of the 
body from the ground, are usually well developed. A series 
of . air-chambers usually exists in powerful fliers. This 
serves a purpose analogous to that of the air-bladder of a 
fish, giving buoyancy. But the most characteristic mark 
of a bird, as above stated, is its feathers, universally present 
and never found outside the class. Like the scales of 
lizards, and probably derived from similar structures, the} 
are of different forms, and serve a variety of purposes. 
The larger ones, with powerful shafts, and forming the tail, 
act as a rudder. Those of the wings give great expanse 
with but little increase in weight, and are so constructed 
that upon the down-stroke they offer great resistance to 
the air, and push the bird forward, while in the reverse 
direction the air slips through them readily. In flight 
these movements of the wing may be too rapid for us to 
follow, as in the humming-birds, though they are usually 
much slower, two to five hundred a minute in many power- 
ful fliers, such as the ducks, and frequently long-continued 
enough to carry them many hundreds of miles at a single 
flight. The remaining feathers are soft and downy, giving 
roundness to the body and enabling it to cleave the air with 
greater ease, and, being poor conductors of heat, they aid in 
keeping the body at the high temperature characteristic of 
birds. In most birds the body is not uniformly clothed in 
feathers. Naked spaces, usually hidden, intervene between 
the feather tracts, and on the feet and toes scales exist. 

190. Molting. — As we all know, the growth of feathers, 
unlike that of hair and nails, is limited, and after they have 
become faded and worn out they are shed, and new ones 



THE BIRDS 203 

arise to take their place. This process of molting is 
usually accomplished gradually, without diminishing the 
powers of flight ; but in the ducks and some other birds all 
the wing- and tail-feathers drop out simultaneously, leaving 
the bird to escape its enemies by swimming and diving. 
The molting-process usually takes place in the fall, after 
the nesting and care for the young is over, and often when 
the need for a heavy winter coat commences to be felt. 
Many birds also don what are called courting colors, ruffs, 
crests, and highly colored patches, in the spring, previous 
to the mating season, doubtless for the purpose of attract- 
ing or impressing their mates. In other cases the change 
appears to be related to the bird's surroundings. A most 
beautiful example of this is the ptarmigans — grouse-like 
birds living far to the north. During winter they are per- 
fectly white and are almost invisible against the snow ; but 
in the spring, as the snow disappears, the white feathers 
gradually fall out and new ones arise. The latter so har- 
monize "with the lichen-colored stones among which it 
delights to sit, that a person may walk through a flock of 
them without seeing a single bird/' 

There are also numerous birds, chiefly those that go in 
flocks, which possess what are known as color-calls or recog- 
nition-marks. These may consist of various conspicuous 
spots or blotches on different parts of the head or trunk, 
such as we see in the yellowhammer or meadow-lark ; or 
one or more feathers of the wings or tail may be strikingly 
colored, as in many sparrows and warblers. During the 
time the bird remains at rest these usually are concealed 
under neighboring feathers, but during flight they are 
strikingly displayed. It may possibly be true, as many 
have urged, that these color-signals are for the purpose 
of enabling various members of the flock to readily follow 
their leader; but this and many other interesting questions 
regarding the color of birds and other animals have not yet 
received final answers. 



201 ANIMAL FORMS 

In very many animals, fishes as well as birds, the tints 
on the under side of the body are usually relatively light 
colored, shading gradually into a darker tint above. This 
is in all probability a protective device, as was recently 
shown by Mr. A. H. Thayer, an American artist. His ex- 
periments show that the light from above renders the back 
less dark, and that the shadow beneath is neutralized by 
the light color. The bird thus appears uniformly lighted, 
and this effect, together with streaks and blotches, renders 
them invisible at surprisingly short distances. 

191. Skeleton. — Turning now to the internal organization 
of birds, we find many points in common with other verte- 
brates, especially the reptiles, but many interesting modifi- 
cations are also present that adapt them for flying and for 
collecting their food. According to the nature of the food, 
the beak may have a great variety of forms. The skull may 
be thick and heavy, or thin and fragile, but these are mat- 
ters of proportion of the various parts possessed by all 
birds. The neck also is of differing length ; but it is in the 
trunk region that the greatest changes have arisen, as we 
may see in any of our ordinary birds. For example, the 
vertebrae of this part of the body are more or less fused 
together into rigid framework, to which are attached the 
ribs that in turn unite with the breast-bone. In the fliers 
the latter bears a vertical plate or keel, to which the great 
muscles that move the wings are attached. The tail con- 
sists, like that of the old-fashioned birds, of several verte- 
brae, but these are of small size and fused together into a 
little knob that supports the tail-feathers. The fore limbs 
are used for flight, but there are the same bones that exist 
in the fore limbs of other vertebrates — one for the upper 
arm, two for the lower, a thumb carrying a few feathers, 
and known as the bastard wing, and indications of several 
bones that form the hand. In the hind limb the resem- 
blance is equally apparent, though its different parts are 
of relatively large size to support the body. It is interest- 



THE BIRDS 



205 



ing to note that the knee has been drawn far up into the 
body, and that the joint above the foot is in reality the 
ankle. 

We thus see that the bird's skeleton presents the same 
general plan as that of the lizard, for example ; but in order 
to combine the elements of strength, lightness, and com- 
pactness essential to successful flight, it has been necessary 
to remodel it to a considerable degree. 

192. Other internal structures. — The lungs of birds con- 
sist of two dark-red organs buried in the spaces between the 
ribs along the back. Each communicates with extensive 
thin-walled air-sacs extending into the space between the 



spL pm 



cbL 




intnal. 

r/lS X 
ml y cm. 



apiur 

apmfffii 

pnlyijh 

coe: pn%^ X0-\i pcd. 

Fig. 120.— Anatomy of a bird, au., auricle ; cbl. and crb.h., cerebellum and cerebral 
hemispheres (divisions of the brain) ; duo., intestine (with portion removed) ; 
r/iz., gizzard; kd., kidney; r.lng., lung; t/\, trachea or windpipe; vent, ven- 
tricle. 



various organs, and in many birds of flight they even extend 
into the bones of the body, and thus decrease their weight. 
" The enormous importance of this feature to creatures 
destined to inhabit the air will be readily understood when 
we learn that a bird with a specific gravity of 1.30 may 
have this reduced to only 1.05 by pumping itself full of air." 
As we know, air is taken into the body in order that the 
oxygen it contains may combine with the tissues of the 
body to liberate the energy necessary for the work of its 



206 ANIMAL FORMS 

life. The deeper and more frequent the breathing the 
greater the amount of energy produced. Birds habitually 
breathe deeper breaths than other animals. The air pass- 
ing into the body traverses the entire extent of the lung 
on its way back to the air-sacs, with the result that large 
quantities of oxygen are taken into the body. This is dis- 
tributed by a circulatory system of a more highly developed 
type than in any of the preceding groups of animals. The 
ventricles of the heart no longer communicate with each 
other, and the pure and impure blood never mingle. Fur- 
thermore, the beating of the heart is comparatively rapid, 
rushing the oxygen as fast as it enters the blood to all por- 
tions of the body. The result is that everywhere heat is 
being generated, so necessary to life and activity. 

In the lower animals no special means are employed to 
husband the energy thus produced, but in the birds the 
body is jacketed in a non-conducting coat of feathers which 
prevents its dissipation. For this and other reasons the 
birds, summer and winter, maintain an even and relatively 
high temperature (102°-110°). Like the mammals, birds 
are warm-blooded animals, full of energy, restlessly active 
to an extent realized in few of the cold-blooded animals. 

193. Digestive system. — This life, at high pressure, de- 
mands a relatively large amount of food to make good the 
losses due to oxidation. The appetites of some growing- 
birds is only satiated after a daily meal equal to from one 
to three times their own weight, and after reaching adult 
size the amount of daily food required is probably not less 
than one-sixth their weight. The nature of the food is 
exceedingly varied, and the digestive tract and certain ac- 
cessory structures are obviously modified in accordance 
with it. The beak, always devoid of teeth in the living- 
form, varies extremely according to the work it must per- 
form. The same is true of the tongue, and many correlated 
modifications exist in the digestive apparatus. In the 
birds of prey and the larger seed-eating species, such as the 



THE BIRDS 207 

pigeons and the domestic fowls, the esophagus dilates into 
a crop, in which the food is stored and softened before being 
acted upon by the gizzard. The latter is the stomach, pro- 
vided with muscular walls, especially powerful in the seed- 
eaters, and with an internal corrugated and horny lining 
which, in the absence of teeth, serves to crush the food. In 
some species, such as the domestic fowls and the pigeons, 
this process is aided by the grinding action of pebbles 
swallowed along with the food. The remaining portions, 
with pancreas and liver, vary chiefly in length, and are 
sufficiently shown in Fig. 120 to require no further descrip- 
tion. 

194. Nesting-habits. — A few birds, such as the ostriches 
and terns, merely scoop a hollow in the earth, and make no 
further pretense of constructing a nest. On the other 
hand, some birds, such as the humming-birds and pewees, 
build wonderful creations of moss, lichens, and spider-webs, 
lining it with down, and concealing it so skilfully that 
they are not often found. Every bird has its own particular 
ideas as to the fitness of its own nest, and the results are 
remarkably different, and form an interesting feature in 
studying the habits of birds. Usually the female takes 
upon herself the choice of the nest and its construction ; 
but these duties are in some species shared by the male. 
After the eggs are laid, the male may also aid in their 
incubation, or may carry food to the female. In other 
species — for example, the pigeons and many sea-birds — the 
parents take turns in sitting upon the eggs and in the sub- 
sequent care of the young. Finally, there are certain birds, 
such as the cuckoo and cowbirds, which take advantage of 
the industry of other species and deposit an egg or two in 
the nests of the latter. All the work of incubation and 
care of the young is assumed by the foster-parents, which 
sometimes neglect their own offspring in their desperate 
attempts to satisfy the appetites of the rapidly growing and 
unwelcome guests. 



208 ANIMAL FORMS 

The eggs of birds are relatively large, and are often 
delicately colored. In some species the blotches and streaks 
of different shades are probably protective, as in the plovers 
and sandpipers, whose eggs blend perfectly with their sur- 
roundings, but many other cases exist not subject to such 
an explanation. 

The young require a high degree of heat for their devel- 
opment, and this is usually supplied by the parent. In a 
very general way the length of sitting, or incubation, is 
proportional to the size of the egg, being from eleven to 
fourteen days in the smaller species, to seven or eight weeks 
in the ostriches. Before hatching, a sharp spine develops 
on the beak, and with this the young bird breaks its way 
through the shell. Among the quails, pheasants, plovers, 
and many other species, the young are born with a covering 
of feathers, wide-open eyes, and the ability to follow their 
parents or to make their own way in the world. Such 
nestlings are said to be precocial^ in distinction to the altrical 
young of the more highly specialized species, such as the 
sparrows, woodpeckers, doves, birds of prey, and their allies, 
which are born helpless and depend for a considerable time 
on the parents for support. 

Some of the owls, crows, woodpeckers, sparrows, quails, 
etc., remain in the same localities where they are bred. 
They are resident birds. The greater number, at the ap- 
proach of winter, migrate toward the southern warmer 
climes, some species traveling in great flocks, by day or 
night, and often at immense heights. In some cases this 
movement appears to be directly related to the food-supply ; 
but there are many apparent exceptions to such a theory, 
and it is possible that many birds migrate for other reasons. 
Certain species migrate thousands of miles, along fairly 
definite routes, the young, sometimes at least, guided by 
the parents, which in turn appear to remember certain 
landmarks observed the year before. Sea-birds, in their 
journeys northward or southward, keep alongshore, occa- 



THE BIRDS 209 

sionally veering in to get their bearings or to rest, espe- 
cially in the presence of fogs. 

195. Classification. — Most zoologists make two primary 
divisions of the living types of birds — those like the ostrich 
with flat breast-bones, and the other the ordinary birds, in 
which the breast-bone has a strong keel for the attachment 
of the powerful muscles used in flight. This distinction is 
not of high importance, but we may use it as a convenience 
in the description of a few typical forms belonging to sev- 
eral orders into which these two divisions are subdivided. 

196. The ostriches, etc. (Ratitse). — From specimens in- 
troduced or from pictures we are doubtless familiar with 
the ostriches and with some of their relatives. The African 
ostrich (Struthio camelus, Fig. 121) is the largest of living 
birds, attaining a height of over seven feet, and is further 
characterized by a naked head and neck, two toes, and 
fluffy, plume-like feathers over parts of the body. They 
are natives of the plains and deserts of Africa, where they 
travel in companies, several hens accompanying the male. 
When alarmed, they usually escape by running with a swift- 
ness greater than that of the horse, but if cornered they 
defend themselves with great vigor by means of their 
powerful legs and beaks. Their food consists of insects, 
leaves, and grass, to which is added sand and stones for 
grinding the food, as in the domestic fowl. The American 
ostriches or rheas, are smaller ostrich-like birds, living on 
the plains of South America. Their habits are essentially 
the same as those of the African species. 

197. The loons, grebes, and auks (Pygopodes). — The birds 
in this and some of the following orders are aquatic in 
their habits. All have broad, boat-like bodies, which, with 
the thick covering of oily feathers, enables them to float 
without effort. The legs are usually placed far back on 
the body — a most favorable place for swimming, but it ren- 
ders such birds extremely awkward on land. The grebes 
are preeminently water-birds. The pied-billed grebe or dab- 




• two-toed ostrich (Struthio camelus). Photograph by Wil- 
liam Gkaiiam. 



THE BIRDS 211 

chick (Podilymbus podiceps), for example, found abundantly 
on the larger lakes and streams throughout the United 
States, captures its food, sleeps, and breeds without leaving 
the water. The loons living in the same situations as the 
dabchick are also remarkable swimmers and divers. Of 
the three species found in this country, the common loon 
or diver ( Gavia imher) attains a length of three feet, and is 
otherwise distinguished by its black plumage, mottled and 
barred with white, which is also the color of the under 
parts. The auks, murres (see frontispiece), and puffins are 
marine, and, like their inland relatives, are expert swim- 
mers and divers, strong fliers, and spend much of their 
time on the open sea. During the breeding-season they 
assemble in vast numbers on rugged cliffs along the shore, 
and lay their eggs on the bare rock or in rudely constructed 
nests. 

198. The gulls, terns, petrels, and albatrosses (Longi- 
pennes). — The birds belonging to this group are among the 
most abundant along the seacoast, and several species make 
their way inland, where they often breed. All are char- 
acterized by long, pointed wings and pigeon or swallow-like 
bodies, which are carried horizontally as the bird waddles 
along when ashore. Many are excellent swimmers and 
powerful fliers, especially the petrels and albatrosses, which 
sometimes travel hundreds of miles at a single flight. 

The gulls are abundantly represented along our coasts, 
where they frequently associate in companies, usually rest- 
ing lightly on the surface of the water, or wheeling lazily 
through the air on the lookout for food. The terns are 
of lighter build than the gulls and are more coastwise in 
their habits, and are further distinguished by plunging like 
a kingfisher for the fishes on which they live. Both the 
gulls and terns breed in colonies, every available spot over 
acres of territory being occupied by their nests, which are 
usually built of grass and weeds placed on the ground. 

The petrels and albatrosses are at home on the high 



212 



ANIMAL FORMS 



seas, rarely coming ashore except at the breeding-season. 
Some species of the former are abundant off our shores? 
especially the stormy petrel (Procellaria pelagica) or Mother 
Carey's chickens ( Oceanites oceanicus)^hio}i are often seen 
winging their tireless flight in the wake of ocean vessels. 
Among the dozen or so albatrosses few reach our shores. 
The wandering albatross (Diomedea exulans), celebrated in 
story and as the largest sea-bird (fourteen feet between the 
tips of its outstretched wings), is an inhabitant of the 
southern hemisphere, and only rarely extends its journeys 
to more northern regions. 

199. Cormorants and pelicans (Steganopodes). — The cor- 
morants and pelicans are comparatively large water-birds 




Fig. 122.— White pelicans (P. erythrorhynchus) and whooping-crane (Grus ameri- 
cana). Photograph by W. K. Fisher. 



usually abundant along the seashore and in many sections 
of the United States. The cormorants or shags are glossy 



THE BIRDS 213 

black in color, with hooked bills, long necks, and short 
wings, which give them a duck-like flight. The much 
larger pelicans (Fig. 122) are at once distinguished by long 
bills, from which is suspended a capacious membranous sac 
All these birds are sociable in their habits, breeding, roost- 
ing, and fishing in great flocks. Their food consists of 
fishes, which the shags pursue under water and capture in 
their hooked beaks ; while the pelicans, diving from a con- 
siderable height or swimming rapidly on the surface, use 
their pouches as dip-nets. The nests, usually built of sea- 
weed or of sticks, are placed on rocky cliffs or on the 
ground in less elevated places. 

200. Ducks, geese, and swans (Lamellirostres). — The birds 
of this order, with their broad, flat, serrated beaks, short 
legs, and webbed feet, are well known, for in a wild or 
domesticated state they extend all over the earth. All are 
excellent swimmers, many dive remarkably well, and are 
strong on the wing. While a considerable number breed 
within the United States, their nesting-grounds are gener- 
ally farther north, and in the early spring it is not unusual 
to see them migrating in flocks from their warmer winter 
homes. Among the ducks, the mergansers, mallards (from 
which our domestic species have been derived), the teals, 
and the beautiful wood-duck remain with us the year 
round, dwelling on quiet streams and shallow ponds, living 
on fish, Crustacea, and seeds. In the more open waters of the 
larger lakes and along the seacoast we find the canvasback, 
the scaup-ducks, and the eiders (Fig. 123) which supply the 
famous down of commerce. Of the few species of geese 
which inhabit the United States, the Canada goose (Br ant a 
canadensis) is perhaps the most familiar. During their 
migrations to the nesting sites they fly in V-shaped flocks, 
their " honks " announcing the opening of spring. The 
brant (B. iernicla) is also common in the eastern part of 
the country, where it, like its relations, lives on vegetable 
substances entirely. The swans are familiar in their semi- 





p IQ 123.— American eider-duck (Somateria drmeri). 



THE BIRDS 215 

domesticated state, but the two beautiful wild swans found 
in this country are rarely seen. 

201. The herons and bitterns (Herodines).— The herons 
and bitterns are also aquatic in their habits, but, unlike the 
swimming-birds, they seek their food by wading. Adapting 
them for such an existence, the legs and neck are usually 
very long, and the bill, longer than the head, is sharp and 
slender. Among the relatively few species in the United 
States, the great blue heron (Arclea herodias) is widely dis- 
tributed, and may often be seen standing motionless in 
some shallow stream on the lookout for fish, or it may 
wander away into the meadows and uplands to vary its diet 
with frogs and small mammals. Even more familiar is the 
little green heron or poke {Ardea virescens), which also is 
seen widely over the country. The night-herons, as their 
name indicates, stalk their prey by night, and during the 
day roost in companies — a characteristic common to most 
herons. The bitterns or stake-drivers are at home in reedy 
swamps, where they live singly or in pairs, and throughout 
the night, during times of migration, utter a booming noise 
resembling the driving of a stake into boggy ground. As 
a rule, the herons breed as they roost — in companies — build- 
ing bulky platforms, usually in trees. The bitterns, on the 
other hand, secrete their nests on the ground in the rushes 
of their marshy home. 

202. Cranes, rails, and coots (Paludicolse). — In their ex- 
ternal form the cranes and rails resemble the herons, but 
in their internal organization they differ considerably. 
They likewise inhabit marshy lands, but usually avoid 
wading, picking up the frogs, fish, and insects or plants 
along the shore or from the surface of the water. The cranes 
are comparatively rare in this country, yet one may occasion- 
ally meet with the whooping-cranes (Grus americana) and 
sand-hill cranes (Gmis mexicana), especially in the South 
and West. They are said to mate for life, and annually 
repair to the same breeding-grounds, where they build their 

15 



216 ANIMAL FORMS 

nests of grass and weeds on the ground in marshy places. 
The rails are more abundant, though rarely seen on ac- 
count of their habit of skulking through the swamp 
grasses. Only rarely do they take to the wing, and then 
fly but a short distance, with their legs dangling awk- 
wardly. Closely related to them are the coots or mud-hens 
(Fulica americana), which may be distinguished, however, 
by their slaty color, white bills, and lobed webs on the toes, 
and consequent ability to swim. All over the United 
States they may be seen resting on the shores of lakes or 
quiet streams, or swimming on the surface gathering food. 
The nest consists of a mass of floating reeds, which the 
young abandon almost as soon as hatched. 

203. The snipes, sandpipers, and plovers (Limicolse). — The 
snipes, sandpipers, and plovers are usually small birds, 
widely scattered throughout the country wherever there 
are sandy shores and marshes. In most species the legs 
are long, and in connection with the slender, sensitive bill 
fit the bird for picking up small animals in shallow water 
or probing for them deep in the mud. During the greater 
part of the year they travel in flocks, but at the nesting- 
season disperse in pairs and build their nests in shal- 
low depressions in the earth. The eggs are usually 
streaked and spotted, in harmony with their surroundings, 
as are the young, which leave the nest almost as soon as 
hatched. 

Fully fifty species of these shore-birds live within the 
confines of the United States. Among these the woodcock 
(Philohela minor) and snipe {Gallinago delicaia) are abun- 
dant in many places inland, where they probe the moist soil 
for food, and in turn are eagerly sought by the sportsman. 
Even more familiar are the sandpipers and plovers, which 
are especially common along the seacoast, and are also 
abundantly represented by several species far inshore. 
Among the latter are the well-known spotted sandpiper or 
"tip-up" {Actitis macularia) and the killdeer plover (^Egi- 



THE BIRDS 



217 



alitis vocifera), which inhabit the shores of lakes and 
streams throughout the country. 

204. Quail, pheasants, grouse, and turkeys (Gallinae). — The 

quail, grouse, and our domestic fowls are all essentially 




Fig 



124.— California quail {Lophortyx californicus). Two-thirds natural size. 

ground-birds, and their structure well adapts them to such 
a life. The body is thick-set, the head small, and the beak 
heavy for picking open and crushing the seeds and berries 



218 ANIMAL FORMS 

upon which they live. The legs and feet are stout, and 
fitted for scratching or for running through grass and 
underbrush. Protective colors also prevent detection, but 
if close pressed they rise into the air with a rapid whirring 
of their stubby wings, and after a short flight settle to the 
ground again. During the breeding-season the male usu- 
ally mates with a number of hens, which build rough nests 
in hollows in the ground, where they lay several eggs. The 
young are precocial. 

The quail or bob-white (Colinus virginianus) and the 
ruffed grouse (Bonasa umbellus) occur throughout the 
Eastern States. Over the same area the wild turkey 
(Meleagris gallopavo) once extended, but is now almost 
extinct. The prairies of the middle West support the 
prairie-hen (Tympanuclias americanus), and the valleys 
and mountains of the far West are the home of several 
species of quails, some of which are beautifully crested. 

205. Pigeons and doves (Columbae). — The pigeons and 
doves belong to a small yet well-defined order, with upward 
of a dozen representatives in the United States. They are 
of medium size, with small head, short neck and legs, and 
among other distinguishing characters frequently possess a 
swollen, fleshy pad in which the nostrils are placed. In 
former years the passenger-pigeon (Ectopistes migratorius), 
inhabiting eastern Xorth America, was probably the most 
common species in this country. Their flocks contained 
thousands, at times millions, of individuals, which often 
traveled hundreds of miles a day in search of food, to return 
at night to definite roosts — a trait which enabled the hunter 
to practically exterminate them. At present the mourning- 
or turtle-dove (Zenaidura macroura) is the most familiar 
and wide-spread of the wild forms. The domestic pigeons 
are all descendants of the common rock-dove (Columha 
livia) of Europe, the numerous varieties such as the tum- 
blers, fantails, pouters, etc., being the product of man's 
careful selection. In the construction of the nest, usually 



THE BIRDS 219 

a rude platform of twigs, and in the care of the young 
both parents have a share. The young at hatching are 
blind, naked, and perfectly helpless, and are fed masticated 
food from the crops of the parents until able to subsist on 
fruits and seeds. 

206. Eagles, hawks, owls, etc. (Raptores). — The birds of 
prey, all of which belong to this order, are carnivorous, 
often of large size and great strength, and are widely dis- 
tributed throughout this country. The vultures live on 
carrion, some of the small hawks and owls on insects, while 
the majority capture small birds and mammals by the aid of 
powerful talons. In every case the beak is hooked, and the 
perfection of the organs of sight and hearing is unequaled 
by any other animal, man included. They live in pairs, 
and in many species mate for life. As a rule, the female 
incubates the eggs, and the male assists in collecting 
food. 

Among the vultures, the turkey-buzzard ( Oathartes aura) 
is most abundant throughout the United States, especially 
in the warmer portions, where it plays an important part 
as a scavenger. Of the several species of hawks, the white- 
rumpecl marsh-hawk {Circus liudsonias), the red-tailed 
hawk (Buteo dorealis), the red-shouldered hawk (Bideo 
Uneatus), and above all the bold though diminutive spar- 
row-hawk (Falco sparverius) are the most abundant and 
familiar. In the more unsettled regions live the golden 
eagle (Aquila chrysaetus) and bald eagle (Haliaetus leuco- 
cephahis). The owls are nocturnal, and not so often seen 
as the other birds of prey, yet the handsome and fierce 
barn or monkey-faced owl (Strix pratincola), and the larger 
species, such as the great gray owl {Scotiaptez cinereua), 
and the beautiful snowy owl [Nyctea nyctea\ are more or 
less common, and occasionally seen. Much more abundant 
is the little screech-owl (Megascops asio), and in the West- 
ern States the burrowing-owl {Speotyto cunicularia), which 
lives in the burrows of the ground-squirrels and prairie- 



220 



ANIMAL FORMS 



dogs. Fiercest and strongest of the tribe is the great 
horned owl {Bubo virginianus). 







Fig. 125. Bald eagle (Haliaetus leucocephalus). 

207. Cuckoos and kingfishers (Coccyges).— Omitting the 
order of parrots (Psittaci), whose sole representative in this 
country is the almost exterminated Carolina parrakeet 



THE BIRDS 221 

(Contents carolvnensis), we next arrive at the cuckoos and 
kingfishers, which differ widely in their habits. The black- 
or yellow-billed cuckoos or rain-crows are shy, retiring 
birds, with drab plumage, and though seldom seen are often 
fairly abundant, and are of much service in destroying 
insects. Unlike their shiftless European relatives, which 
lay their eggs in the nests of others birds, they build their 
own airy homes in some bush or hedgerow, and raise their 
brood with tender care. The belted kingfisher (Ceryle 
alcyon) is also of a retiring disposition, and spends much 
of its time on some branch overlooking the water, occa- 
sionally varying the monotony by dashing after a fish, or 
flying with rattling cry to another locality. Their nests 
are built in holes in banks, and six or eight young are 
annually reared. 

208. The woodpeckers (Pici). — The woodpeckers are 
widely distributed throughout the world, and are preemi- 
nently fitted for an arboreal life. The beak is stout for 
chiseling open the burrows of wood-boring insects, which are 
extracted by the long and greatly protrusible tongue. The 
feet, with two toes directed forward and two backward, are 
adapted for clinging, and the stiff feathers of the tail serve 
to support the bird when resting. Almost all are bright- 
colored, with red spots on the head, at least in the males, 
which may further attract their mates by beating a lively 
tattoo with their beaks on some dry limb. The glossy 
white eggs are laid in holes in trees, and both parents are 
said to share the duties of incubation and feeding the 
young. Among the more abundant and well-known species 
is the yellowhammer or flicker (Colaptes aiiratus), which 
extends throughout the United States. Somewhat less 
widely distributed is the red-headed woodpecker (Melaner- 
pes eryihroceplialus), and the small black-and-white downy 
woodpecker (Dryobates pubescens). This is often called 
sapsucker, but incorrectly so, as, like all but one of our other 
woodpeckers it feeds on insects. The yellow-bellied wood- 



222 



ANIMAL FORMS 



pecker (Spliyrapicus varius) is a real sapsucker, living on 
the juices of trees. A close relative of the red-headed 
woodpecker, the California woodpecker (Melane?yes formi- 
civorus), is renowned for its habit of boring holes in bark 
and inserting the acorns of the live oak. Subsequently the 
bird returns, and breaking open the acorns, devours the 
grubs which have infested them, and apparently eats the 
acorns also. 

209. Swifts, humming-birds, etc. (Macrochires). — The birds 
of this order are rapid, skilful fliers, and their wings are 
very long and pointed. The feet, on the other hand, are 




Fig. 126.— Night-hawk {Chordeiles virginianus) on nest. Photograph by II. K. Job. 

small, relatively feeble, and adapted for perching or cling- 
ing. Accordingly, the insects upon which they feed are 
taken during flight by means of their open beaks. The 
night-hawk (Chordeiles virginianus), roosting lengthwise on 
a branch by day, at nightfall takes to the wing, and high 
in the air pursues its food after the fashion of a swallow. 
In the same haunts throughout the United States the whip- 



THE BIEDS 223 

poorwill (Antrostomus vociferus) occurs, sleeping by day, 
but active at night. Neither of these birds constructs nesl s, 
but lays its streaked and mottled eggs directly on the 
ground. The chimney-swifts (ChcBtura pelagica), swallow- 
like in general form and habits, but very unlike the swallows 




Fig. 127.— Anna hummers (one day old), showing short bill and small size of body. 
Compare with last joint of little finger. 

in structure, frequent hollow trees or unused chimneys, to 
which they attach their shallow nests. The nearly related 
humming-birds are chiefly natives of tropical America, only 
a few species extending into the United States. Of these 
the little, brilliantly colored, and pugnacious ruby throat 
(Troehilus colubris) is the most widely distributed. Its 
nest, like that of other hummers, is composed of moss and 
lichens bound together with cobweb and lined with down. 

210. Perching birds (Passeres). — The remaining birds, 
over six thousand in all, belong to one order, the Passeres 
or perchers. They are characterized by great activity, 
interesting habits, frequently by exquisite powers of song, 
and in addition to several other structural arrangements 
have the feet adapted for perching. Their nesting habits 



224 



ANIMAL FORMS 



differ widely, but in every case the young are helpless at 
the time of hatching, and require the care of the parents. 

The perchers constitute the greater number of the birds 
living in the meadows and woods, and are more or less 




Fig. 128.— Anna hummer (Calypte anna) on nest. 

common, and consequently familiar everywhere. Among 
the families into which the order is divided that of the fly- 
catchers (Tyrannidce), the crows and jays (Corvidce), the 
orioles and blackbirds {Icteridce), the finches and sparrows 
(Fringillidce), the swallows (Hirundinidce), the warblers 
(Mniotiltidce), the thrushes, robins, and bluebirds ( Turdidce), 
are the more familiar, though the others are equally inter- 
esting. 



CHAPTER XVIII 

THE MAMMALS 

211. General characteristics. — The mammals, constituting 
the last and highest class of the vertebrates, comprise such 
forms as the opossum and kangaroo, the whales and por- 
poises, hoofed and clawed animals, the monkeys and man. 
All are warm-blooded, air-breathing animals, having the 
skin more or less hairy. The young are born alive, except 
in the very lowest forms, which lay eggs like reptiles, and 
for some time after birth are nourished by milk supplied 
from the mammary glands (hence the word mammals) of 
the mother. The skeleton is firm, the skull and brain 
within are relatively large, and, with few exceptions, four 
limbs are present. 

Most of the mammals inhabit dry land. A number, 
however, such as the whales and seals, are aquatic ; while 
others, such as the beavers, muskrats, etc., though not 
especially adapted for an aquatic life, are, nevertheless, 
active swimmers, and spend much of their time in the 
water. 

Mammals tend to associate in companies, as we may 
witness among the ground-squirrels, prairie-dogs, rats, 
mice, and the seals and whales. In many cases they band 
for mutual protection, and often fight desperately for one 
another. Claws, hoofs, and nails are efficient weapons, and 
spiny hairs, as on the porcupines, bony plates, such as 
encircle the bodies of the armadillos, and thick skin and 
hair, serve as a protection. The hair is also frequently 
colored to harmonize the animal with its surroundings. 

225 



226 ANIMAL FORMS 

Some rabbits and hares in the far north don a white coat 
in the winter season. 

212. Skeleton. — As in other vertebrates, the external 
form of mammals is dependent in large measure upon the 
internal skeleton. This consists of relatively compact 
bones, the cavities of which are filled with marrow. Those 
forming the skull are firmly united, and, as in other verte- 
brates, afford lodgment for several organs of special sense 
and for the brain, which, like that of the birds, completely 
fills the cavity in which it rests. The vertebral column to 
which the skull is attached differs considerably in length, 
but it invariably gives attachment to the ribs, and to the 
basal girdles supporting one or two pairs of limbs. Gener- 
ally speaking, the number of bones in the head and trunk 
of all mammals is the same, so the variations we note in 
the species about us, for example, are simply due to differ- 
ences of shape and proportion. As we are aware, there is a 
great dissimilarity between the length of the neck of man 
and that of the giraffe, yet the number of bones in each 
is precisely the same. On the other hand, the variations 
occurring in the limbs are often due to the actual disap- 
pearance of parts of the skeleton. Five digits in hand 
and foot is the rule, and yet, as we well know, the horse 
walks on the tip of its middle finger and toe, the others 
being represented by small, very rudimentary, splint bones 
attached far up the leg. The even-hoofed animals walk on 
two digits, two smaller hoofed toes being often plainly 
visible a short distance up the leg, as in the pig. In the 
whales the hind limbs have completely disappeared, and in 
the seals, where the fore limbs are modified, as in the 
whales, into flippers, the hind limbs show many signs of 
degeneration. 

213. Digestive system. — Some mammals, such as man, 
monkeys, and pigs, are omnivorous ; others, like the cud- 
chewers and gnawers, are vegetarians ; and still others, 
like the foxes, weasels, and bears, are carnivorous. In 



TIIE MAMMALS 227 

every case the food substances are acted on by a digestive 
system constructed on the same general plan as that in man, 
yet modified according to the specific work it is required to 
perform. The teeth especially afford a valuable indication 
of the animal's feeding habits, and, as we may notice later. 
are also of much value in classification. They consist of 
incisors used in biting, canines for tearing, and premolars 
and molars for crushing and grinding. 

The remaining portions of the digestive tract, esopha- 
gus, stomach, and intestine, with their appended glands, are 
usually not unlike these possessed by the squirrel (Fig. 1). 
The chief differences are in the size of the various regions. 
The stomach, for example, may be long and slender or of 
great dimensions, and its surface may further be increased 
by several lobes, which are especially well developed in the 
ruminants or cud-chewers. The intestine, relatively longer 
in the mammals than in any other class of vertebrates, also 
exhibits great differences in length and size. In the flesh- 
eating species its length is about three or four times the 
length of the body, while in the ruminants it is ten or 
twelve times the length of the animal. 

214. Nervous system and sense-organs. — As before noted, 
the nervous system of mammals is characterized by the 
large size and great complexity of the brain. Even in the 
simpler species the cerebral hemispheres (large front lobes 
of the brain, Fig. 1) are well developed, and in the higher 
forms of the ascending series they form by far the larger 
part of the brain. The sense-organs also are highly de- 
veloped, and are constructed and located much as they are 
in man. The greatest variations occur in the eyes. In 
some of the burrowing animals they are usually small, and 
in some of the moles and mice may even be buried beneath 
the skin and very rudimentary. On the other hand, they 
are large and highly organized in nocturnal animals ; more 
so, usually, than in those which hunt their prey by day. 
The ears also have different grades of perfection, which 



228 ANIMAL FORMS 

appear to be correlated with the habits of the animal. 
Among the species of subterranean habits the sense of hear- 
ing is largely deficient ; but, on the other hand, it is ex- 
ceedingly keen in the ruminants, and enables them to detect 
their enemies at surprisingly great distances. In these 
creatures the outer ears are of large size and great mobility, 
and, placed as they are on the top of the head, serve to con- 
centrate the sound-waves on the delicate apparatus within. 
In the mammals the sense of smell reaches its highest de- 
velopment, especially among the carnivores which scent their 
prey. On the other hand, it is said to be absent in the 
whales and very deficient in the seals. The sense of taste, 
closely related to that of smell, is located in taste-buds on 
the tongue, and is also more acute than in any other class of 
animals. The sense of touch, located over the surface of 
the body, is especially delicate on the tips of the fingers, 
the tongue, and lips, which often bear long tactile hairs, 
called whiskers or vibrissa. 

215. Mental qualities. — Correlated with the high degree 
of perfection of the brain and sense-organs the mammals 
show a higher degree of development of the intellectual 
faculties than any other class of animals. In many cases 
their acts are instinctive, and not the result of previous 
training and experience. Just as the duck hatched in an 
incubator instinctively takes to the water and pecks at its 
food, or as the bee builds its symmetrical comb, many of 
the mammals perform their duties day by day. On the 
other hand many other mammals are also undoubtedly in- 
telligent. They possess the faculty of memory ; they form 
ideas and draw conclusions ; they exhibit anger, hatred, and 
self-sacrificing devotion for their companions and offspring 
that is different from that in man only in degree and not 
in kind. In fact, intelligence differs from instinct primar- 
ily in its power of choice among lines of action. 

216. Classification. — Of the eleven orders into which the 
mammals have been divided eight are represented in this 




Fig. 129.— Three-toed sloth {Bradypus). About one-tenth natural size. 



230 



ANIMAL FORMS 



country. Of the other three the first (Monotremes) and 
simplest of the eleven is represented by the duck-mole 




Fig. 130.— Australian duck-mole (Ornithorhynchus paradoxus). One-fifth natural 

size. 



{Omithorliynchus) living in the Australian rivers. Its 
general appearance and mode of life are represented in 



THE MAMMALS 



231 



Fig. 130. The duck-moles are the only mammals which 
lay eggs. One egg a year is deposited in a carefully con- 
structed nest where the young are hatched. Another order 
{Edentata) includes a number of South and Central Ameri- 
can forms, among which are the ant-eaters, armadillos, 
and tree-inhabiting sloths (Fig. 129). Still another order 
(Sirenia) includes the fish-shaped marine dugong and sea- 
cows or manatees, of which one species is found occasion- 
ally on the Florida coast. The remaining orders are de- 
scribed in the succeeding sections. 

217. The opossums and kangaroos (Marsupialia). — The 
lowest order of mammals represented in the United States 




Fig. 131.— Opossum (Didelphys virginiana). One-tenth natural size. Photograph 
by W. H. Fisher. 

is that of the marsupials. It includes the opossums and 
kangaroos, together with a number of comparatively small 
and unfamiliar animals living chiefly in and about Australia. 
16 



232 ANIMAL FORMS 

The opossums, fairly abundant throughout the warmer 
portions of this country, are rat-like creatures, with scaly 
tails, yellowish-white fur, large head, and pointed snout. 
Except at the breeding season they lead solitary lives, 
sleeping in the holes of trees by day and at night feeding 
on roots, birds, and fruits. 

The kangaroos, familiar from specimens in menageries 
or museums, chiefly inhabit the plains of Australia. The 
giant gray kangaroos (Macropus giganteus); attaining & 
height of over six feet, go in herds, and owing to the great 
development of their hind limbs and tails are able, when 
alarmed, to travel with the swiftness of a horse. Several 
smaller species, some no larger than rabbits, live among 
the brush, and like their larger relatives crop the grass and 
tender herbage with sharp incisor teeth. 

AVhile the marsupials do not lay eggs as does the duck- 
mole, they allow them to develop within the body for a 
very short time only. Hence the young, when born, are 
scarcely more than an inch in length, and are blind, naked, 
and perfectly helpless. At once they are placed by the 
mother in the pouch of skin, or marsupium, on the under 
side of her body. In this the young are suckled and pro- 
tected until able to gather their oavh food and fight their 
own way. 

218. Rodents or gnawers (Glires). — The rodents are a 
large group of mammals, including such forms as the rats, 
mice, squirrels, gophers, and rabbits. They arc readily dis- 
tinguished by their clawed feet adapted for climbing or 
burrowing, and by large curved incisor teeth. Unlike 
ordinary teeth, they grow continually, and, owing to the 
restriction of the hard enamel to their front surfaces, wear 
away behind faster than in front, thus producing a chisel- 
like cutting edge. 

The largest of our native rodents is the porcupine 
(Erethizon dorsatus), which ranges from Maine to Mexico, 
and attains a Length of nearly three feet. Many of the hairs 



THE MAMMALS 



233 



of the body have the form of stiff, barbed spines (Fig. 132), 
readily dislodged so that the animal requires no other w<a_ 
pon of defense. The rabbits and hares are of smaller size, 
and the cottontails especially are widely distributed. West 
of the Mississippi the jack-rabbits are familiar, and are 




Fig. 132.— Porcupine (Hysti'ix cristata). One-tenth natural size.— After Breiim. 

famous for their great speed. Like the porcupines, they 
feed on leaves and grass, and are often very destructive. 
The mice, especially the field and white-footed mice, are 
abundant in woodland and meadow throughout the United 
States. The house-mouse (Mils musculus) is a native of 
Europe, as is the common rat (M. decumanus), which was 
imported over a century ago. The wood-rat (Xeotoma), 
however, is native, and may be found in many localities 
from east to west. The muskrat (Fiber zibethicus)^ beaver 
(Castor canadensis), and woodchuck (Arctomys monax) were 
also more or less plentiful formerly, but in many localities 
are well-nigh exterminated. The squirrels, on the other 
hand, continue to exist in large numbers. The prairie- 



234 ANIMAL FORMS 

dogs, ground-squirrels, and chipmunks of the terrestrial 
species are of frequent occurrence, and of the tree-dwellers 
the fox, gray and red squirrels are well known in many 
sections of the United States. 

219. Insect-eating mammals (Insectivora). — The shrews 
and moles belonging to this order are representatives of a 
large group of small animals, which, unlike the major 
number of rodents, live on insects. The shrews, of which 
there are several species in this country, are small, mouse- 
like creatures, nocturnal in their habits, and hence rarely 
seen. The moles are of much larger size, and owing to 
their burrowing proclivities scarcely ever appear above 
ground, but excavate elaborate burrows with their shovel- 
like feet, devouring the insects which fall in their way. The 
common mole (Scalops aquaticus) extends from the eastern 
seaboard to the Mississippi Eiver, where it is replaced by 
the prairie-mole (S. argenteiis), which extends far to the 
west, into a country inhabited by other species. 

220. The bats (Cheiroptera). — The bats are also insectiv- 
orous, but their habits are widely different from those of 
the shrews and moles. The forearm and the fingers of the 
fore limbs are greatly elongated, and are connected by a 
thin papery membrane, which also includes the hind limbs 
and tail, and serves as an efficient organ of flight. During 
the day they remain suspended head downward in some 
dark cranny, awakening at nightfall to capture flying 
insects. Several species are found in this country, the 
most common being the little brown bat ( Vespertilio fus- 
cus), with small, fox-like face, large erect ears, and short 
olive-brown hair. The red bat (Lasiurus borealis) is also 
plentiful everywhere throughout the United States, and is 
distinguished from the preceding by its somewhat larger 
size and long reddish-brown fur. 

221. The whales and porpoises (Cete). — The animals 
belonging to this order, the whales (Fig. 133), porpoises, and 
dolphins, are aquatic animals bearing a resemblance to fishes 



THE MAMMALS 



235 



only in external form. The cylindrical body has no distinct 
neck, the comparatively large head uniting directly with 



■\ 












| 


• 


rf^. 


i 







s 



\ 








the cylindrical body, which terminates in the tail with hori- 
zontally placed fins. Xo external signs of hind limbs exist, 



236 ANIMAL FORMS 

while the fore limbs are short and capable of being moved 
only as a whole. External ears are also absent. The eyes 
are exceedingly small, those of individuals attaining a length 
of from fifty to eighty feet, being in some species, at least, 
but little larger than those of an ox. These are often placed 
at the corners of the mouth. The nasal openings, often 
known as blow-holes, are situated on the forehead, and as 
the whale comes to the surface for air afford an outlet for 
the stream of breath and vapor often blown high in the 
air — a process known as spouting. In some of the whales, 
such as the dolphin, porpoise, and sperm-whales, the teeth 
persist throughout life, but in most of the larger species 
they never " cut " the gum, but early disappear, and their 
place is taken by large numbers of whalebone plates with 
frayed edges which act as strainers. The smaller-toothed 
forms (porpoises, dolphins, and several species of grampus) 
are frequently seen close to the shore, where they are usu- 
ally actively engaged in capturing fish. On the other hand, 
the larger species, such as the humpback, right whale, and 
sulfurbottom, not uncommon along our coasts, especially 
to the northward, live on much smaller organisms. With 
open mouth these whales swim through the water until 
they collect a sufficient quantity of jelly-fishes, snails, and 
Crustacea, then closing the mouth strain out the water 
through the whalebone fringes and swallow the residue. 

As noted above, the animals of this order are almost 
wholly devoid of hair, but the heat of the body is retained 
by a thick layer of fat beneath the skin. This "blubber" 
also gives lightness to the body (as do the voluminous lungs), 
and, furthermore, yields large quantities of oil, which in 
former times made " whale-fishing " a profitable industry. 
The whales bear one, rarely two offspring, which are solicit- 
ously attended by the mother for a long time. The smaller 
species grow to a length of from five or eight feet (por- 
poises, dolphins) to twice this size (grampuses) ; while the 
larger whales, by far the largest of animals, range from 



THE MAMMALS 237 

thirty to over a hundred feet in length with a weight of 
many tons. 

222. Hoofed mammals (TJngulata). — The order of hoofed 
animals or ungulates includes a large number of forms like 
the zebra, elephant, hippopotamus, giraffe, deer, and several 
other wild species, some of which are domesticated, such 
as horses, sheep, goats, and cattle. All of these animals 
walk on the tips of their toes, and the claws have become 
developed into hoofs. The order is divided into the odd- 
toed forms (perissodactyls), such as the rhinoceros witli 
three toes and the horse with one, and the even-toed (artio- 
dactyls), as the pigs with four, and the ox, deer, etc., with 
two toes. The even-toed forms are again divided into 
those which chew the cud (ruminants) and those w^hich do 
not (non-ruminants). Xo living native odd-toed mammal 
exists in this country, and of the wild even-toed species all 
are ruminants. In the members of this latter group the 
swallowed food passes into a capacious sac (the paunch), is 
thoroughly moistened, and passed into the second division 
(the honeycomb), later to be regurgitated and ground by 
the powerful molars. It is then reswallowed, and under- 
goes successive treatment in the other two divisions of 
the stomach (the manyplies and reed) before entering the 
intestine. 

Among the Xorth American ruminants, the deer fam- 
ily (Cervidce) is the best represented. In the more unsettled 
regions of the East the red deer is still common, and the 
same may be said of the white-tailed, black-tailed, and 
mule-deer of the West. Among the woods and lakes to 
the northward live the reindeer and caribou, and the largest 
of the deer family, the moose, which attains the size of the 
horse. Of nearly the same size is the wapiti or elk, whose 
general characters are shown in Fig. 134. In all of the 
above-mentioned species the horns, if present, are confined 
to the male (except in the reindeer), and are annually shed 
after the breeding season. 











I 






THE MAMMALS 239 

The native hollow-horned ruminants (Bovidce) are at 
present confined to the Western plains, and comprise the 
pronghorn antelope (Antilocapra americana)^ the wary big- 
horn or Eocky Mountain sheep (Ovis canadensis), living 
in mountain fastnesses, and the buffalo or bison {Bison 
Mson) : All of these species were formerly abundant. 
especially the pronghorn and buffalo, which roamed the 
plains by thousands, but their extermination has been 
nearly complete, small herds only persisting in a few wild, 
inaccessible regions, or protected in parks. 

Our domestic sheep and cattle are probably the descend- 
ants of several wild species living in Europe and other 
portions of the world. Of the domesticated even-toed 
ungulates the horse is the direct descendant of Asiatic 
wild breeds ; while the pig traces its ancestry back to the 
wild boar (Sus scrofa) of Europe, and probably a native 
species (S. indicas) of eastern Asia. 

'223. Flesh-eating mammals (Ferae). — The order of Ferce 
or Carnivora is typically exemplified by such animals as the 
lions, tigers, bears, dogs, cats, and seals, forms which differ 
from all other mammals by the large size of the canine teeth 
(often called dog-teeth) and the molars, which are adapted 
for cutting, not crushing. The limbs, terminated by four 
or five flexible digits, bear well-developed claws, which, to- 
gether with the teeth, serve for tearing the prey. While 
the bears shuffle along on the soles of their feet, the greater 
number of species, as illustrated by the dog and cat, tread 
noiselessly on tiptoe. Almost all are fierce and bold, with 
remarkably keen senses and quick intelligence, and are the 
dreaded enemies of all other orders of mammals. 

The largest land-inhabiting carnivora are the bears, of 
which the brown or cinnamon bear (Ursus americanus)^ 
inhabiting Xorth America generally where not extermi- 
nated, and the huge grizzly ( Ursus horribilis) of the West- 
ern mountains, are the best-known species. The former 
lives on berries and juicy herbs, w T hile the grizzly prefers 



240 



ANIMAL FORMS 



the flesh of animals which it kills. The raccoon (Fig. 135) 
(Procyon lotor) is found in wooded districts all over the 
United States, and its general appearance and thieving 
propensities are well known. Almost everything is accept- 







able as an article of food, and its fondness for poultry and 
vegetables makes it an unmitigated nuisance. The otters, 
skunks, badgers, wolverenes, sables, minks, and weasels, while 
differing considerably in general appearance and habits, nev- 



THE MAMMALS 241 

ertheless belong to one family (the weasel family, Mustelida), 
and are more or less valued for their fur. Almost all are 
characterized by a fetid odor, especially the skunk, .which 
is notoriously offensive, and in consequence is avoided by 
all other animals. 

The dog family is represented by several widely distrib- 
uted varieties of the red fox ( Vulpes pennsylvanicus) and 
gray fox ( Urocyon cinereo-argentatus), and by the coyotes 




Fig. 13G. — Silver fox (Vulpes pe?inS7jlvanicus, var. cw'gentatus). Photograph 
by W. K. Fisher. 

(Canis latrans) and wolves (Cants nubilus). The domestic 
dog ( Canis familiaris) is probably the descendant of the 
wolf, and owing to man's careful breeding during thou- 
sands of years has formed several widely differing varieties. 
The cat family, comprising the most powerful, savage, 
and keenest-scented carnivora, is represented by the lion, 
tiger, jaguar, and hyena. In this country the group is 
represented by the lynx (Lynx canadensis), the wildcat 
( Lynx rufus), and the panther or puma (Felis concolor), 
which attains the length of nearly five feet. The domestic 
cat has, like the dog, been domesticated for centuries, and 
has possibly descended from an African species (Felts 




Fig. 137.- Panthers (F<!h< ooncolor) and peccaries; {Dicotyles torquatus). 



THE MAMMALS 



243 



caff r a), which was held sacred by the Egyptians, who em- 
balmed them by thousands. 

824 Man-like mammals (Primates). — The last and high- 
est order of mammals, the Primates, includes the lemurs, 
monkeys, and man. The first of these are strange squir- 
rel-like forms living chiefly in trees in Madagascar and 
neighboring regions where they feed on insects. The apes 
and monkeys are divided into Old and New World forms, 
which differ widely from each other. The American species 
are marked by flat noses, with the nostrils far apart. All are 
arboreal, many have long prehensile tails, and the digits bear 
nails, not claws. Among them are several species of marmo- 
sets, the howling monkeys (Myocetes), the spider-monkeys 
(Ateles), and the capuchins (Cebus), all of which are more or 
less common in captivity. In the Old World apes, on the 
other hand, the nostrils are close together and are directed 
downward, the tail is never 
prehensile, and in some cases 
is rudimentary,and may even 
disappear. The lowest spe- 
cies (the dog-like apes) in- 
clude the large, clumsy ba- 
boons, among them the fa- 
miliar blue-nosed mandrill 
(Cynocephalus maimon) and 
several other species of light- 
er frame, such as the long- 
tailed monkey (Cercopithe- 
cus) (Fig. 139), the tailless 
Macacus, common in menag- 
eries, and the Barbary ape, in- 
habiting northern Africa and 
extending over into Spain. 

The remaining anthro- 
poid or man-like apes include the gibbons (Hyloiates)^ orang- 
utan (Simia), gorilla (Gorilla), and chimpanzee (Antliropo- 




Fig. 138.— Baby orang-utan. From life. 




Pig. 189.— A monkey | Cercopithecus) in a characteristic attitude of watchfulness 



THE MAMMALS 



245 



pithecus). The gibbons, inhabiting southeastern Asia, pos- 
sess arms of such length that they are able to touch their 
hands to the ground as they stand erect. They are thus 
adapted for a life in the trees, where they spend most of their 
time feeding on fruit, leaves, and insects. In the same dis- 
trict the orang occurs, walking when on the ground on its 
knuckles and the sides of its feet. It prefers the life in 
the trees, however, in 
which it builds nests 
serving for rest and 
concealment. The go- 
rilla (Fig. 140), the 
largest of apes, attain- 
ing a height of over 
five feet, and a weight 
of two hundred 
pounds, is a native of 
Africa, where it lives 
in families and sub- 
sists on fruits. The 
same region is the 
home of the chimpan- 
zee, which in its vari- 
ous characteristics ap- 
proaches most nearly 
f to man. 

Man (Homo sapi- 
ens) is distinguished 

by the inability to oppose the big toe as he does his thumb — 
a feature associated with his erect position — and by the rela- 
tively enormous size of the brain. Even in an average four- 
year-old child or an Australian bushman the brain is twice as 
large as in the gorilla. With this relatively great develop- 
ment of the nervous system is correlated superior mental 
faculties, which together with social habits and powers of 
speech exalt man to a position far above the Inchest ape. 




Fig. 140.— Gorilla (Gorilla). 






246 ANIMAL FORMS 

As usually understood, the family of man (Homi?iidce) 
contains but a single species, cosmopolitan and highly vari- 
able. This species is " now split up into many subspe- 
cies or races, the native man of this continent, or ' Ameri- 
can Indian,' being var. americanus. Other races now 
naturalized in America are : the Caucasian race, var. euro- 
pceus ; the Mongolian race, var. asiaticus ; and the negro 
race, afer. The first of these is an immigrant from Europe, 
the second from Asia, and the third was brought hither 
from Africa by representatives of var. europceus to be used 
as slaves." 






CLASSIFICATION OF ANIMALS 

The following table of classification is designed to show the systematic position 
of the more important animals mentioned in the text. 

ANIMAL KINGDOM 

One-celled Animals : 

Branch I. PROTOZOA (protos, first; zoon, animal) 
Class I. Rhizop oda {rhiza, root; pous, foot). 

Amoeba, Difflugia. 
Class II. Infusoria (organisms found in infusions). 
Order 1. Flagella'ta (flagellum, a whip). 

Euglena, Coddsig'a, Pandori'na, Vol'vox. 
Order 2. Cilia'.ta (cilium, an eyelash). 
Paramos' cium, Vorticel'la. 

Many-celled Animals (Metazoa) : 

Branch II. PORIF ERA (porus, pore ; fero, to carry) 
Class I. Porifera (or sponges). 

Branch III. CGELENTERA TA (animals with combined body and 

stomach cavity) 
Class I. Hydrozo'a (hydra, water-serpent ; zoon, animal). 

Hydra, Gonione mus, Hydractin'ia, Portuguese man-of-war. 
Class II. Scyphozo a (scyphos, cup; zoon, animal). 

Bhizos'toma, HaUclys'tus. 
Class III. Actinozo'a (actis, a ray ; zoon, animal). 

Branch IV. PLATYHELMIN THES * (platus, flat; helminthos, 

a worm) 
Class I. Plato'da (platus, flat; eidos, likeness). 
Plana via, Leptopla'na. 

* For purposes of convenience, the flatworms (Platyhelminthes), 
roundworms (Xematelminthes), and segmented worms (Annelids) are 
combined in one branch (The Worms) in the text. 

17 247 



248 ANIMAL FORMS 

Class II. Tremato da {trematodes, pierced with holes, from the 
erroneous belief that the suckers are holes into the body). 

Liver fluke, JEpidel'la. 
Class III. C est 6 da {cestos, a girdle ; eidos, likeness). 

Tapeworm. 

Branch V. NEMATELMINTHES {nema, thread; helmintlws, a 

worm) 
Class I. Nemato da. 

Vinegar eel (Anguillula), Trtchi'na, horsehair snake (Gordius). 

Branch VI. NEMERTIN EA {?iemejies, a sea-nymph) 

Branch VII. ROTIF ERA (rota, a wheel; fero, to carry) 

Branch VIII. ANNELIDA (annelus, a ring) 
Class I. Chaetop oda (chaite, bristle; pons, foot). 
Order 1. Polychae te {polus, many ; chaite, bristle). 

Ner'eis, Poly no' e, Ser'pula, Sabel'la. 
Order 2. Oligochae te (oligos, few; chaite, bristle). 
Earthworm {Lum 1 bricus). 
Class II. Hirudin ea (hirudo, a leech). 

Leeches. 
Class III. Gephyrea {gephura, a bridge, because these animals were 
once supposed to bridge the gap between the worms and sea- 
cucumbers). 

Branch IX. MOLLUSCOI DA 
Class I. Polyzo a {polns, many ; zoon, animal— colonial animals). 

Polyzoa, sea-mats. 
Class II. Brachiop oda {brachion, arm; pons, foot). 

Lamp-shells (brachiopods). 

Branch X. MOLLUS'OA'^o/^, soft) 
(lass I. Lamellibranchiata {lamella, a plate ; branchia, gill). 

Clams, mussels, oysters, ship-worm {Teredo). 
Class II. Gastropoda (gaster, stomach; pons, foot). 

Snails, slugs, armadillo snails, naked snails, nudibranchs. 
Class III. Cephalbp oda (cephale, head; pons, foot). 

Squids, cuttlefishes, devil-fishes {Oc'topns), nautilus. 

Branch XL ECHINODER MAT A (ecMnos, a hedgehog; derma, 

skin) 
Class I. Asteroi dea {aster, star; eidos, likeness). 
Starfishes. 



CLASSIFICATION OF ANIMALS 249 

(lass II, Ophiuroi dea (ophis, serpent; oura, tail; eidos, likeness). 

Serpent- or brittle-stars, basket-stars. 
(lass 111. Holothuroi dea (holothurion, a kind of water polyp; 
eidos, likeness). 

S^a-cucumbers. 
Class [V. Crinoi dea (erinon, lily; eidos, likeness). 

Sea-iilies or crinoids. 
Class V. Echinoi dea (echinos, hedgehog; eidos, likeness). 

Sea-urchins. 

Branch XII. ARTHROP ODA (artliron, joint ; pous, foot) 
Class I. Crusta cea (crusta, a crust or shell). 

Fairy-shrimp (BrancMp 'us), water-fleas (Dapli'nia), cop'epod, 
Cyclops, goose barnacle, acorn barnacle, Saccul'% na, opossum- 
shrimp, prawn, lobster, crayfish, cancer-crab, rock-crab, pill- 
bug or i'sopod, sand-hopper or amphi'pod. 
Class II. Onycoph ora (onyx, claw ; phero, to carry). 

Peripetias). 
Class III. Myriop oda (myrios, numberless; pous, foot). 

Cent'iped, thousand-legs. 
Class IY. Insec'ta (insectum, cut in, owing to the grooves surround- 
ing the body). 
Fishmoth, springtail, cockroach, grasshopper, cricket, katydid, 
locust, dragon-fly, caddis-fly, may-fly, white ants or termites, 
ant-lion, water-boatman, water-bug, back-swimmer, chinch- 
bug, squash-bug, lice, plant-lice, Phylloxera, scale-insect, 
gnat, mosquito, flea, house-fly, stag-beetle, wood-beetle, water- 
beetle, potato-beetle, ladybug, firefly, moth, butterfly, ants. 
honey-bees and bumblebees, wasps, hornets, yellow-jackets. 
Class V. Arach nida (arachne, spider). 

Garden-spider, tarantula, bird-spider, trap-door spider, mite, 
tick, king-crab or horseshoe crab. 

Branch XIII. CHORDATA (chorda, a cord, referring to the 
notochord) 
Subbranch I. Adelochor da. Class Adelochorda. 
Subbranch II. Urochor da. Class Urochorda. 

Sea-squirts, Tunica'ta, Ascid'ians. 
Subbranch III. Vertebra ta (vertebratus, jointed). 

Division A. Acra'nia (a, without : cranion, skull). Class Lepto- 
cardii. 
Lancelet (Branchios'toma = Amphiox'us). 
Division B. Crania t a. 



250 ANIMAL FORMS 

Class I. Cyclostomata (cyclos, circle ; stoma, mouth). 
Hagfishes, lamprey. 

Class II. Pis'ces (piscis, fish). 

Shark, skate or ray, lung-fish, sturgeon, garpike, catfish, horned 
pout, bullhead, carp, dace, chub, minnow, eel, herring, shad, 
salmon, trout, pike, stickleback, blindfish, sea-horse, mullet, 
flying-fish, perch, darter, sunfish, sea-bass, mackerel, snapper, 
grunt, weakfish, bluefish, rose-fish, gurnard, sculpin, codfish, 
flounder, angler. 

Class III. Amphibia (amphi, double ; bios, life). 

Siren, mud-puppy, water-dog, tiger salamander, axolotl, toad, 
frog, tree-frog. 

Class IV. Reptil'ia (reptans, creeping). 

Skink, " glass-snake,'' swift, chameleon, horned toad, Gila mon- 
ster, blacksnake, grass-snake, milk-snake, rattlesnake, copper- 
head, water-moccasin, soft-shell turtle, snapper, painted turtle, 
box-turtle, leather-turtle, loggerhead, hawkbill, crocodile, alli- 
gator. 

Class V. A'ves (avis, bird). 

Ostrich, loon, grebe, auk, murre, puffin, gull, tern, petrel, alba- 
tross, cormorant, pelican, duck, goose, swan, heron, bittern, 
crane, rail, mud-hen or coot, snipe, woodcock, sandpiper, kill- 
dee plover, quail, grouse, wild turkey, prairie-chicken, pigeon, 
dove, eagle, hawk, owl, turkey-buzzard, cuckoo, kingfisher, 
woodpecker, sapsucker, swift, humming-bird, night-hawk, 
whippoorwill, crow, jay, swallow, warbler, thrush, robin, 
bluebird. 

Class VI. Mammalia (mamma, breast). 

Duck-mole, ant-eater, sloth, armadillo, sea-cow, opossum, kanga- 
roo, porcupine, mouse, rat, muskrat, woodchuck, beaver, rabbit, 
squirrel, chipmunk, prairie-dog, shrew, mole, bat, whale, gram- 
pus, dolphin, porpoise, zebra, elephant, giraffe, deer, antelope, 
goat, sheep, horse, cow, pig, buffalo, bear, raccoon, otter, skunk, 
badger, wolverene, sable, mink, weasel, dog, fox, wolf, cat, 
lynx, panther, monkey, ape, baboon, gibbon, orang-utan, 
gorilla, chimpanzee, man. 



I N D E X 



Acipenser sturio (illus.), 162. 

Acorn-barnacle (illus.), 97. 

Air-bladder, 155. 

Albatross, 212. 

Alligator mississippie?isis (illus.), 

191. 
Alternation of generations, 35. 
Altricial, 208. 
Amoeba (illus.), 12; structure and 

habits, 12. 
A moeba- like protozoa, 12. 
Amphibian, development of, 174; 

distribution, 178 ; anatomy and 

habits, 179. 
Amphibious (amphi, double; bios, 

life). 176. 
Amphioxus (illus.), 157. 
Amphipod (illus.), 106. 
Anatomy (anatemno, to cut up), 

defined, 1. 
Angler (illus.), 169. 
Angle-worm (illus.), 55. 
Anguillula aceti (illus.). 53. 
Animals, characteristics of. 2 : sim- 
ple and complex, 18. 
Animals and plants compared, 2. 
Annelids, 55. 

Anosia plexippus (illus.), 125. 
Ant. 128: white (illus.). 120. 
Anteater. 231. 
Antedon (illus.), 148. 
Antelope, 239. 



Ant-lion (illus.), 120. 

Apes, 243. 

Arachnida, characteristics of, 133. 

Arclueopteryx, 201. 

Argynnis cybele (illus.), 126. 

Ariolimax columbianus (illus.), 81. 

Armadillo, 231. 

Arthropods, general features of, 

93. 
Ascidian (illus.), 152. 
Asexual reproduction, 31. 
Asterias ocracea (illus.). 141. 
Astrophyton (illus.), 143. 
Auk, 209. 
Axolotl, 183. 

Back-swimmer, 121. 
Balancers, 122. 
Band-worm (illus.), 70. 
Barnacles (illus.), 96. 
Bascanion constrictor (illus.), 187. 
Basket-star (illus.), 141. 
Bass, 166. 

Bat. brown. 234; red, 234. 
Bear. 239. 
Beaver. 232, 
Bees, 238. 
Beetles. 124. 

Bell animalcule (illus.), 16. 
Bilateral symmetry. 44. 
Biology (bios, life: logos, a dis- 
course) defined, 1. 

251 



252 



ANIMAL FORMS 



Birds, characteristics of, 201 ; anat- 
omy of, 204 ; habits of, 207. 

Bird spider, 136. 

Bittern, 215. 

Black-snake (illus.), 193. 

Blastula (illus.), 21. 

Bombus (illus.), 130. 

Bony fish (illus.), 160. 

Botany, defined, 1. 

Brachiopod (illus.), 70. 

Bradypus tridactylus (illus.), 229. 

Brancliiostoma califomiense (il- 
lustration), 157. 

Branchipus (illus.), 94. 

Brittle-star (illus.), 141 ; regenera- 
tion of, 145. 

Bugs, 121. 

Bumblebee (illus.), 130. 

Butterflies, 125. 

Buzzard, 219. 

Byssus, 77. 

Caddis-fly, 119. 

Calcolynthus primigenius (illus.), 

25. 
Calypte anna (illus.), 224. 
Cancer productus (illus.), 104. 
Caprella (illus.), 106. 
Carapace, of Crustacea, 95, 99 ; of 

turtle, 188. 
Carp, 163. 

Cat, domestic, 239 ; wild, 239. 
Catfish, 163. 
Cell (cella, a little room), 7; shape 

and size, 7; typical (illus.), 8. 
Centipeds (illus.), 111. 
Cephalopod (illus.), 87. 
Cephalothorax, 99. 
Cercopithecus (illus.), 244. 
Cervu8 canadensis (illus.), 238. 
Cestode (illus.), 50. 
Cete, 234. 



Cheiroptera, 234. 

Chelonia, 188. 

Chinch-bug, 122. 

Chiton (illus.), 82. 

Chologaster avetus (illus.), 164 ; C. 
agassizi (illus.), 164. 

Chordate, characteristics of, 151. 

Chordeiles virginianus (illus.), 
222. 

Chub, 163. 

Cilium (ahum, an eyelash), 16. 

Circulatory system, use of, 4. 

Clam (illus.), 72 ; anatomy, 72, 78 ; 
rock- and wood-boring, 75. 

Clitellum, 58. 

Coccyges, 220. 

Cockroach, 118. 

Coelenterates, general character- 
istics of, 18. 

Coleoptera (illus.), 124. 

Columbae, 210. 

Complex animals, characteristics 
of, 18. 

Compound eyes, 109. 

Coot, 215. 

Copperhead, 193. 

Corals (illus.), 41. 

Cormorant, 212. 

Correlation of function and struc- 
ture, 6. 

Cottontail, 233. 

Courting colors, 203. 

Crab, hermit (illus.), 102 ; cancer 
(illus.), 103; rock (illus.), 104; 
fiddler, 104. 

Crane (illus.), 215. 

Crayfish (illus.), 101. 

Cricket, 118. 

Crinoid (illus.). 143. 

Crocodile, 190. 

Crocndilia (illus.). 190. 

Crotalus adamanteus (illus.), 222. 



1XDEX 



253 



Crustacea, 93 ; anatomy of, 98, 107 ; 

multiplication of , 98, 110. 
Cteniza (illus.), 137. 

Cuckoo. 220. 
Cucumaria (illus.), 146. 
Cuticle, 14. 

Cuttlefish, 87. 
Cutworm. 112. 
Cyclops (illus.), 95; anatomy of. 

*98. 
Cvclostomes, 157. 



Decapods, 102. 
Deer, 222. 

Dendrostoma (illus.), 68. 

Devil-fish (illus.), 87. 

Didelphys virginiana (illus.), 231. 

Diemyctylus torosus (illus.), 182. 

Digestive tract, use of, 3. 

Diptera (illus.), 119. 

Division of labor, 21. 

Dog, 223. 

Dolphin, 221. 

Dove, 205. 

Dragon-fly (illus.), 118. 

Duck-mole (illus.), 216. 

Ducks (illus.), 200. 

Eagle, golden, 205; bald (illus.), 
205. 

Earthworm (illus.), 55: anatomy, 
55 ; distribution, 59. 

Echinoderms, 141 ; locomotor sys- 
tem, 146 ; development of, 150. 

Ecology, 1. 

Eel, 163. 

Egg, fertilization of, 20, 21. 

Elk (illus.), 222. 

Encystment of protozoa, 13. 

Epialtus produdus (illus.), 104. 

EpideUa squamula (illus.), 49. 



Eretmocltelys imbricata (illus.), 

195. 
Esox (illus.), 165. 
Euglena (illus.), 1 7. 
Eurypelma lentzii (illus.), 186. 

Fairy shrimp (illus.), 94. 

Felis concolor (illus.), 242. 

Fera), 239. 

Firefly, 124. 

Fish, general characters of, 154 ; 

respiration, 155 ; anatomy, 168 ; 

breeding habits, 171. 
Fishmoth, 117. 
Fish-worm (illus.), 55. 
Flagellum (flagellum, a whip), 14. 
Flea, 122. 
Flicker, 221. 

Flies, 122 ; development of, 123. 
Flounders, 168. 
Fox (illus.), 241. 
Frog, 178. 

Gammarus (illus.), 106. 

Gallime, 217. 

Ganglion {ganglion, a swelling), a 
swelling of the nerve-cord due 
to the accumulation of nerve- 
cells, 79. 

Ganoidea, 161. 

Garpike, 161. 

Garter-snake, 193. 

Gasteropod (illus.), 80; anatomy and 
physiology, 81. 

Gastric mill (illus.), 107. 

Gastrula (diminutive of gaster, 
stomach), 21. 

Geese, 213. 

Gelasimus (illus.), 104. 

Gephyrean worms (illus.), 67. 

Gila monster (illus.), 193. 

Glass-snake, 191. 



254 



ANIMAL FORMS 



Glires, 232. 

Gnat, 122. 

Gonionemus vertens (illus.), 34. 

Goose barnacle (illus.), 96. 

Gordius, 54. 

Gorilla (illus.), 245. 

Grasshopper (illus.), 117. 

Grebe, 209. 

Green gland, 108. 

Grouse, 218. 

Grits americana (illus.), 212. 

Gull, 211. 

Habitat (habitare, to dwell), 45. 

Hagfish, 157. 

Halicetus leucocephalus (illus.), 
220. 

Haliclystus (illus.), 39. 

Harvestman, 135. 

Hawks, 219. 

Helix (illus.), 81. 

Heloderma suspectum (illus.), 192. 

Hemiptera, 121. 

Heptacarpus brevirostris (illus.), 
101. 

Hermit-crab (illus.), 102. 

Herodines, 215. 

Herons, 215. 

Herring, 163. 

Homo sapiens, 245. 

Honey-bee, 130. 

Hoofed animals, 237. 

Horned toads, 192. 

Hornet, 132. 

Horse-fly (illus.), 119. 

Horsehair-snake, 54. 

Horseshoe-crab (illus.), 139. 

Humming-bird (illus.), 222. 

Hydra, structure of, 29 ; multipli- 
cation of, 31; regeneration of, 
51. 

ITyilractinia (illus.), 36, 103. 



Hydranth, 33. 

Hydrozoa, 34 ; regeneration of, 51. 
Hymenoptera (illus.), 128. 
Hystrix cristata (illus.), 233. 

Incubation (incumbo, to rest upon), 

207. 
Infusoria, 17. 
Insectivora, 234. 
Insects, numbers, 114 ; anatomy, 

115 ; respiration, 117. 
Isopod (illus.), 101. 

Jelly-fish, of Hydrozoa, 33 ; of Scy- 

phozoa, 37. 
Julus (illus.), 112. 

Kangaroo, 232. 
Katydid, 117. 
Keyhole-limpet, 82. 
King-crab (illus.), 139. 
Kingfisher, 221. 

Lacertilia, 185, 
Lamellibranch (illus.), 72. 
Lamellirostres, 213. 
Lamprey (illus.), 157. 
Lamp-shell (illus.), 70. 
Lancelet (illus.), 157. 
Lasso-cell, 30. 
Leeches (illus.), 63 ; haunts and 

habits, 64. 
Lemur. 243. 
Lepas (illus.), 99. 
Lepidoptera (illus.), 125. 
Lepomis megalotis (illus.), 167. 
Leptoplana (illus.), 45. 
Lice, 122. 
Life histories and race histories, 

27. 
Limicolne, 216. 
Limulus polypJiemiis (illus.), 139. 



INDEX 



255 



Littorina, habits of, 83. 

Liver-fluke, 49. 

Lizard (illus.), 185. 

Lobster, 102. 

Locust (illus.), 117. 

Long-horned borer beetle (illus.), 

124. 
Longipennes, 211. 
Loon, 209. 

Lophius piscatorius (illus.), 169. 
Loplwrtyx californicus (illus.), 217. 
Lumbricus ferrestris (illus.), 55. 
Lung-fish, 160. 
Lynx (illus.), 241. 

Macrobdella (illus.), 63. 

Macrocheira, 222. 

Mammals, characteristics of, 225; 
anatomy, 226 ; classification, 228. 

Man, 245. 

Many-celled animals, 11. 

Marsupialia, 231. 

Marsupium {marsupium, a purse 
or bag), 232. 

May-fly, 118. 

Jlegaptera versabilis (illus.), 235. 

Mesenteric filaments, 40. 

Messmates, defined, 48. 

Metamorphosis, retrograde, 99 ; in- 
complete, 126 ; complete, 128. 

Metazoa, defined, 11. 

Mice, 233. 

Millipeds (illus.), 111. 

Minnow, 163. 

Mite (illus.), 138. 

Mole, 234. 

Mollusks, general characters of, 72. 

Molt, of Crustacea, 99, 110; of 
birds, 202. 

Monarch butterfly (illus.), 125. 

Monkeys, 243. 

Morphology, defined, 1. 



Mosquito, 122; development of, 

123. 
Moths (illus.), 125. 
Mud-hen, 215. 
Mud-puppy (illus.), 178. 
Multiplication of animals, 5. 
Muscle-cell (illus.), 7. 
Muscular system, use of, 4. 
Mussel, 77. 

Jlysis americana (illus.), 100. 
Mytilus edulis (illus.), 77. 

Nauplius (illus.), 99. 
Nematoda (illus.), 52. 
Nemertean worm (illus.), 70. 
Nereis (illus.), 59. 
Nerve-cell (illus.), 7. 
Nettle-cell (illus.), 30. 
Neuroptera, 118. 
Newt (illus.), 178. 
Night-hawk (illus.), 222. 
Notochord, 151. 
Nucleus (illus.), 9. 

Octopus punctatus (illus.), 87. 
Oligochaetes, 59. 

Operculum {operculum, a lid), 87. 
Opossum (illus.), 231. 
Opossum-shrimp (illus.), 100. 
Orang-utan (illus.), 243. 
Orb-weaving spider, 136. 
Omitlwrhyncli us paradoxus (illus- 
tration), 230. 
Orthoptera, 117. 
Ostrich (illus.), 209. 
Oyster, 77. 
Owls, 219. 

Pagurus bernliardus (illus.), 103. 
Paludicolae, 215. 

Pandorina (illus.), 19. 
Panther (illus.), 241. 



256 



ANIMAL FORMS 



Paramecium (illus.), 15. 

Parapodium (para, alongside of; 
pons, foot), 60. 

Parasitism, 48. 

Passeres, 223. 

Pelican (illus.), 212. 

Pelicanus erytlirorhynclms (illus.), 
212. 

Perca flavescens (illus.), 155. 

Perch," 166. 

Perching birds, 223. 

Peripatus eiseni (illus.), 111. 

Pheasant, 217. 

Physalia (illus.), 37. 

Physiology (physis, the nature of 
a thing; logos, a discussion), 1. 

Pici, 221. 

Piddock (illus.), 75. 

Pigeons, 218. 

Pike (illus.), 164. 

Pill-bug (illus.), 105. 

Pineal gland, 198. 

Planaria (illus.), 45. 

Plants and animals, differences be- 
tween, 1. 

Plants, characteristics of higher, 2. 

Plant-lice, 122 ; in ant-nests, 120. 

Plastron, 188. 

Plover, killdee, 216. 

Polychaetes, 59 ; sedentary (illus.), 
61 ; development of, 63. 

Poly nee, brevisetosa (illus.), 61. 

Polyzoa (illus.), 68. 

Porcellio scaber (illus.), 105. 

Porcupine (illus.), 232. 

Porpoise, 234. 

Portuguese man-of-war (illus.), 36. 

Prairie-dog, 233. 

Prawn (illus.), 100. 

Precocial birds, 208. 

Primates, 243. 

Proboscis, of flatworms, 46. 



Procyon lotor (illus.), 240. 
Protoplasm (protos, first; plasma, 

anything molded), 9 ; structure 

of, 10. 
Protozoa, 11 ; characteristics of, 

17; colonial, 19. 
Pugettia richii (illus.), 104. 
Pulsating vacuoles, 16, 17. 
Pygopodes, 209. 

Quail (illus.), 217. 

Rabbit, 233. 

Raccoon (illus.), 240. 

Race histories and life histories, 27. 

Radial symmetry, 44. 

Rail, 215. 

Rain-crow, 220. 

Raptores, 219. 

Rat, house-, 233 ; wood-, 233 ; 
musk-, 233. 

Ratitae, 209. 

Rattlesnake (illus.), 191. 

Recognition-marks, 203. 

Regeneration, 51. 

Reproduction, sexual and asexual, 
5,32. 

Reptiles, general characteristics, 
185 ; distribution, 191 ; anat- 
omy, 195. 

Retrograde metamorphosis, 99. 

Rotifer (illus.), m. 

Ruminant, 237. 

Sabella, 62. 

Salamander (illus.), 176; distribu- 
tion, 178 ; structure of, 179. 
Salmon, 163. 
Sand-dollar (illus.), 142. 
Sand hopper (illus.), 105. 
Sandpiper, 216. 
Sapsucker, 221. 



INDEX 



257 



Sarcoptes scabei (illus.), 138. 

Scelophorus undulatus (illus.), 185. 

Scorpion (illus.), 134. 

Scyphozoa, 37 ; development of, 38. 

Sea-anemone, 40. 

Sea-cucumber (illus.), 143 ; regen- 
eration of, 145. 

Sea-lily (illus.), 143. 

Sea-mat (illus.), 68. 

Sea-urchin (illus.), 141. 

Sea-squirt (illus.), 152. 

Sedentary life, effect of, 62. 

Segments, of worms, 55 ; of arthro- 
pods, 94. 

Segmented worms, 55. 

Serpentes, 186. 

Serpent-star (illus.), 141. 

Serphus dilatatas (illus.), 122. 

Serpula (illus.), 62. 

Serpulids, 62. 

Seta, 55. 

Sexual reproduction, 32. 

Shark (illus.), 159. 

Shell-gland, 108. 

Ship worm, 75. 

Shrew, 234. 

Shrimp, fairy, 94 ; opossum (illus.), 
100. 

Silk-moth (illus.), 127. 

Silver-spot butterfly (illus.), 126. 

Simple animals, characteristics of, 
18. 

Single-celled animals, 11. 

Sinus, blood, 78. 

Siren (illus.), 178. 

Slug (illus.), 80. 

Snail, common (illus.), 80; arma- 
dillo (illus.), 82 ; naked (illus.), 82. 

Snakes, 186; distribution of, 193. 

Snipes, 216. 

Somateria dresseri (illus.), 214. 

Species, origin of. 91. 



Sperm-cell, 20. 

Sphenodon punctatus (illus.), 199. 

Spicule, of sponge (illus.), 26 ; of 
coral, 42. 

Spiders, organization of, 135; hab- 
its, 136. 

Spinnerets, 135. 

Spiny-rayed fishes, 166. 

Sponge, development of (illus.). 
21 ; distribution, 22 ; shape and 
structure, 23. 

Spontaneous generation, 54. 

Springtail, 117. 

Squalus acanthias (illus.), 159. 

Squash-bug, 122. 

Squid (illus.), 87. 

Squirrels, 233. 

Starfish (illus.), 140 ; regeneration, 
145 ; structure, 146. 

Steganopodes, 212. 

Stickleback, 164. 

Structure and function, correla- 
tion of, 6. 

Stvongylocentrotus purpuratus (il- 
lustration), 144. 

Struthio camelus (illus.), 210. 

Sturgeon (illus.), 161. 

Sunfish (illus.), 166. 

Symmetry, radial and bilateral, 44. 

Swan (illus.), 213. 

Swift, 222. 

Tcenia solium (illus.), 51. 

Tapeworm (illus.), 50; develop- 
ment, 51 ; in relation to regen- 
eration, 51. 

Tarantula (illus.), 137. 

Teeth, use of, 2. 

Teleostei, 160. 

Termites (illus.), 120. 

Tern. 211. 

Terrapme Carolina (illus.). 189. 



258 



ANIMAL FORMS 



Thousand-legged worms (illus.), 
111. 

Threadworms (illus.), 52. 

Thysanura, 117. 

Tick, 138. 

Tiger salamander, 178. 

Toad (illus.), 178. 

Trap-door spider (illus.), 137. 

Trematode (illus.), 48; develop- 
ment, 51. 

Trichina spiralis (illus.), 53. 

Trigger hair, 31. 

Turkey, 218. 

Turtles, 188; structure, 189; dis- 
tribution, 194. 

Typlilichthys subterraneus (illus.), 
163. 

Ungulata, 237. 

Vacuole, pulsating, 16 ; use of, 17. 
Velum (illus.), 35. 
Vespa, nest of (illus.), 131. 
Vinegar eel (illus.), 53. 
Volvox (illus.), 19 ; multiplication 

of, 20. 
Vertebrates, characteristics of, 145 . 
classification, 143. 



Vorticella (illus.), 16. 

Vulpes pennsylvanicus (illus.), 241. 

Wasps, 128 ; habits of, 131. 
Water-boatman, 121. 
Water-bug (illus.), 121. 
Water-dog (illus.), 178. 
Water-flea, 95. 
Whale, humpback (illus.), 235; 

sperm, 236. 
Whale lice, 107. 
Wheel-animalcule (illus.), 66. 
Wheel- weaving spiders, 136. 
Whippoorwill, 222. 
White ant (illus.), 120. 
Wood-beetle (illus.), 124. 
Woodchuck, 233. 
Woodcock, 216. 
Woodpeckers, 221. 
Worms, general characters of, 44 ; 

classification, 45. 

Yellowhammer, 221. 
Yellow-jacket, 132. 

Zirphma crispata (illus.), 76. 
Zoology, 1. 
Zoophyte, 29. 



(1) 



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